From ac556104c1f84143565918f6cc4b109e38fb6a23 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Wed, 7 May 2025 17:12:57 -0400
Subject: [PATCH 01/23] link to MPI C interface instead of C++

---
 cmake/CMakeLists.txt                      |  7 ++++---
 cmake/Modules/LAMMPSInterfacePlugin.cmake | 19 ++++++++++---------
 cmake/Modules/MPI4WIN.cmake               | 12 ++++++------
 cmake/Modules/Packages/COLVARS.cmake      |  2 +-
 cmake/Modules/Packages/GPU.cmake          |  2 +-
 cmake/Modules/Packages/ML-HDNNP.cmake     |  6 +++---
 6 files changed, 25 insertions(+), 23 deletions(-)

diff --git a/cmake/CMakeLists.txt b/cmake/CMakeLists.txt
index 04ec037184..d21c845bad 100644
--- a/cmake/CMakeLists.txt
+++ b/cmake/CMakeLists.txt
@@ -406,13 +406,14 @@ if(BUILD_MPI)
   if((CMAKE_SYSTEM_NAME STREQUAL "Windows") AND CMAKE_CROSSCOMPILING)
     include(MPI4WIN)
   else()
-    find_package(MPI REQUIRED)
+    enable_language(C)
+    find_package(MPI REQUIRED COMPONENTS C)
     option(LAMMPS_LONGLONG_TO_LONG "Workaround if your system or MPI version does not recognize 'long long' data types" OFF)
     if(LAMMPS_LONGLONG_TO_LONG)
       target_compile_definitions(lammps PRIVATE -DLAMMPS_LONGLONG_TO_LONG)
     endif()
   endif()
-  target_link_libraries(lammps PUBLIC MPI::MPI_CXX)
+  target_link_libraries(lammps PUBLIC MPI::MPI_C)
 else()
   target_sources(lammps PRIVATE ${LAMMPS_SOURCE_DIR}/STUBS/mpi.cpp)
   add_library(mpi_stubs INTERFACE)
@@ -734,7 +735,7 @@ if(PKG_ATC)
     message(FATAL_ERROR "The ATC Package is not compatible with -DLAMMPS_BIGBIG")
   endif()
   if(BUILD_MPI)
-    target_link_libraries(atc PRIVATE ${LAPACK_LIBRARIES} MPI::MPI_CXX)
+    target_link_libraries(atc PRIVATE ${LAPACK_LIBRARIES} MPI::MPI_C)
   else()
     target_link_libraries(atc PRIVATE ${LAPACK_LIBRARIES} mpi_stubs)
   endif()
diff --git a/cmake/Modules/LAMMPSInterfacePlugin.cmake b/cmake/Modules/LAMMPSInterfacePlugin.cmake
index 5b7444f62c..2363937af5 100644
--- a/cmake/Modules/LAMMPSInterfacePlugin.cmake
+++ b/cmake/Modules/LAMMPSInterfacePlugin.cmake
@@ -129,7 +129,8 @@ endif()
 # MPI configuration
 if(NOT CMAKE_CROSSCOMPILING)
   set(MPI_CXX_SKIP_MPICXX TRUE)
-  find_package(MPI QUIET)
+  enable_language(C)
+  find_package(MPI QUIET COMPONENTS C)
   option(BUILD_MPI "Build MPI version" ${MPI_FOUND})
 else()
   option(BUILD_MPI "Build MPI version" OFF)
@@ -163,12 +164,12 @@ if(BUILD_MPI)
 
       ExternalProject_get_property(mpi4win_build SOURCE_DIR)
       file(MAKE_DIRECTORY "${SOURCE_DIR}/include")
-      add_library(MPI::MPI_CXX UNKNOWN IMPORTED)
-      set_target_properties(MPI::MPI_CXX PROPERTIES
+      add_library(MPI::MPI_C UNKNOWN IMPORTED)
+      set_target_properties(MPI::MPI_C PROPERTIES
         IMPORTED_LOCATION "${SOURCE_DIR}/lib/libmsmpi.a"
         INTERFACE_INCLUDE_DIRECTORIES "${SOURCE_DIR}/include"
         INTERFACE_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
-      add_dependencies(MPI::MPI_CXX mpi4win_build)
+      add_dependencies(MPI::MPI_C mpi4win_build)
 
       # set variables for status reporting at the end of CMake run
       set(MPI_CXX_INCLUDE_PATH "${SOURCE_DIR}/include")
@@ -199,12 +200,12 @@ if(BUILD_MPI)
 
       ExternalProject_get_property(mpi4win_build SOURCE_DIR)
       file(MAKE_DIRECTORY "${SOURCE_DIR}/include")
-      add_library(MPI::MPI_CXX UNKNOWN IMPORTED)
-      set_target_properties(MPI::MPI_CXX PROPERTIES
+      add_library(MPI::MPI_C UNKNOWN IMPORTED)
+      set_target_properties(MPI::MPI_C PROPERTIES
         IMPORTED_LOCATION "${SOURCE_DIR}/lib/libmpi.a"
         INTERFACE_INCLUDE_DIRECTORIES "${SOURCE_DIR}/include"
         INTERFACE_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
-      add_dependencies(MPI::MPI_CXX mpi4win_build)
+      add_dependencies(MPI::MPI_C mpi4win_build)
 
       # set variables for status reporting at the end of CMake run
       set(MPI_CXX_INCLUDE_PATH "${SOURCE_DIR}/include")
@@ -212,13 +213,13 @@ if(BUILD_MPI)
       set(MPI_CXX_LIBRARIES "${SOURCE_DIR}/lib/libmpi.a")
     endif()
   else()
-    find_package(MPI REQUIRED)
+    find_package(MPI REQUIRED COMPONENTS C)
     option(LAMMPS_LONGLONG_TO_LONG "Workaround if your system or MPI version does not recognize 'long long' data types" OFF)
     if(LAMMPS_LONGLONG_TO_LONG)
       target_compile_definitions(lammps INTERFACE -DLAMMPS_LONGLONG_TO_LONG)
     endif()
   endif()
-  target_link_libraries(lammps INTERFACE MPI::MPI_CXX)
+  target_link_libraries(lammps INTERFACE MPI::MPI_C)
 else()
   add_library(mpi_stubs INTERFACE)
   target_include_directories(mpi_stubs INTERFACE $<BUILD_INTERFACE:${LAMMPS_SOURCE_DIR}/STUBS>)
diff --git a/cmake/Modules/MPI4WIN.cmake b/cmake/Modules/MPI4WIN.cmake
index 02db6d4744..9c5a2c8b6c 100644
--- a/cmake/Modules/MPI4WIN.cmake
+++ b/cmake/Modules/MPI4WIN.cmake
@@ -21,12 +21,12 @@ if(USE_MSMPI)
 
   ExternalProject_get_property(mpi4win_build SOURCE_DIR)
   file(MAKE_DIRECTORY "${SOURCE_DIR}/include")
-  add_library(MPI::MPI_CXX UNKNOWN IMPORTED)
-  set_target_properties(MPI::MPI_CXX PROPERTIES
+  add_library(MPI::MPI_C UNKNOWN IMPORTED)
+  set_target_properties(MPI::MPI_C PROPERTIES
     IMPORTED_LOCATION "${SOURCE_DIR}/lib/libmsmpi.a"
     INTERFACE_INCLUDE_DIRECTORIES "${SOURCE_DIR}/include"
     INTERFACE_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
-  add_dependencies(MPI::MPI_CXX mpi4win_build)
+  add_dependencies(MPI::MPI_C mpi4win_build)
 
   # set variables for status reporting at the end of CMake run
   set(MPI_CXX_INCLUDE_PATH "${SOURCE_DIR}/include")
@@ -60,12 +60,12 @@ else()
 
   ExternalProject_get_property(mpi4win_build SOURCE_DIR)
   file(MAKE_DIRECTORY "${SOURCE_DIR}/include")
-  add_library(MPI::MPI_CXX UNKNOWN IMPORTED)
-  set_target_properties(MPI::MPI_CXX PROPERTIES
+  add_library(MPI::MPI_C UNKNOWN IMPORTED)
+  set_target_properties(MPI::MPI_C PROPERTIES
     IMPORTED_LOCATION "${SOURCE_DIR}/lib/libmpi.a"
     INTERFACE_INCLUDE_DIRECTORIES "${SOURCE_DIR}/include"
     INTERFACE_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
-  add_dependencies(MPI::MPI_CXX mpi4win_build)
+  add_dependencies(MPI::MPI_C mpi4win_build)
 
   # set variables for status reporting at the end of CMake run
   set(MPI_CXX_INCLUDE_PATH "${SOURCE_DIR}/include")
diff --git a/cmake/Modules/Packages/COLVARS.cmake b/cmake/Modules/Packages/COLVARS.cmake
index b4dc738626..55fbc52abf 100644
--- a/cmake/Modules/Packages/COLVARS.cmake
+++ b/cmake/Modules/Packages/COLVARS.cmake
@@ -28,7 +28,7 @@ endif()
 
 if(BUILD_MPI)
   target_compile_definitions(colvars PUBLIC -DCOLVARS_MPI)
-  target_link_libraries(colvars PUBLIC MPI::MPI_CXX)
+  target_link_libraries(colvars PUBLIC MPI::MPI_C)
 endif()
 
 if(COLVARS_DEBUG)
diff --git a/cmake/Modules/Packages/GPU.cmake b/cmake/Modules/Packages/GPU.cmake
index 6d0ce303a5..f32e97c3eb 100644
--- a/cmake/Modules/Packages/GPU.cmake
+++ b/cmake/Modules/Packages/GPU.cmake
@@ -484,7 +484,7 @@ RegisterFixStyle(${GPU_SOURCES_DIR}/fix_gpu.h)
 
 get_property(GPU_SOURCES GLOBAL PROPERTY GPU_SOURCES)
 if(BUILD_MPI)
-  target_link_libraries(gpu PRIVATE MPI::MPI_CXX)
+  target_link_libraries(gpu PRIVATE MPI::MPI_C)
 else()
   target_link_libraries(gpu PRIVATE mpi_stubs)
 endif()
diff --git a/cmake/Modules/Packages/ML-HDNNP.cmake b/cmake/Modules/Packages/ML-HDNNP.cmake
index 99017f222d..086432c1bf 100644
--- a/cmake/Modules/Packages/ML-HDNNP.cmake
+++ b/cmake/Modules/Packages/ML-HDNNP.cmake
@@ -44,7 +44,7 @@ if(DOWNLOAD_N2P2)
     set(N2P2_PROJECT_OPTIONS "-DN2P2_NO_MPI")
   else()
     # get path to MPI include directory
-    get_target_property(N2P2_MPI_INCLUDE MPI::MPI_CXX INTERFACE_INCLUDE_DIRECTORIES)
+    get_target_property(N2P2_MPI_INCLUDE MPI::MPI_C INTERFACE_INCLUDE_DIRECTORIES)
     foreach (_INCL ${N2P2_MPI_INCLUDE})
       set(N2P2_PROJECT_OPTIONS "${N2P2_PROJECT_OPTIONS} -I${_INCL}")
     endforeach()
@@ -102,9 +102,9 @@ if(DOWNLOAD_N2P2)
   # nnpif library has MPI calls if MPI is enabled, so we must link with MPI libs
   if(BUILD_MPI)
     set_target_properties(LAMMPS::N2P2::LIBNNPIF PROPERTIES
-      INTERFACE_LINK_LIBRARIES MPI::MPI_CXX)
+      INTERFACE_LINK_LIBRARIES MPI::MPI_C)
     if((CMAKE_SYSTEM_NAME STREQUAL Windows) AND CMAKE_CROSSCOMPILING)
-      add_dependencies(LAMMPS::N2P2::LIBNNPIF MPI::MPI_CXX)
+      add_dependencies(LAMMPS::N2P2::LIBNNPIF MPI::MPI_C)
     endif()
   endif()
 

From acd53ebd7cf504bf4ec8f1094f773c17d05fef90 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Wed, 7 May 2025 17:13:36 -0400
Subject: [PATCH 02/23] update flag to accommodate changes in clang

---
 cmake/Modules/Testing.cmake | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/cmake/Modules/Testing.cmake b/cmake/Modules/Testing.cmake
index a72ce17e1b..4862a0d38e 100644
--- a/cmake/Modules/Testing.cmake
+++ b/cmake/Modules/Testing.cmake
@@ -26,10 +26,17 @@ if(ENABLE_TESTING)
         OR ((CMAKE_LINUX_DISTRO STREQUAL "Fedora") AND (CMAKE_DISTRO_VERSION VERSION_GREATER 30)))
       include(CheckCXXCompilerFlag)
       set(CMAKE_CUSTOM_LINKER_DEFAULT default)
-      check_cxx_compiler_flag(-fuse-ld=mold HAVE_MOLD_LINKER_FLAG)
-      check_cxx_compiler_flag(-fuse-ld=lld HAVE_LLD_LINKER_FLAG)
-      check_cxx_compiler_flag(-fuse-ld=gold HAVE_GOLD_LINKER_FLAG)
-      check_cxx_compiler_flag(-fuse-ld=bfd HAVE_BFD_LINKER_FLAG)
+      if((CMAKE_CXX_COMPILER_ID STREQUAL "Clang") AND (CMAKE_CXX_COMPILER_VERSION VERSION_GREATER 19.9))
+        check_cxx_compiler_flag(--ld-path=mold HAVE_MOLD_LINKER_FLAG)
+        check_cxx_compiler_flag(--ld-path=lld HAVE_LLD_LINKER_FLAG)
+        check_cxx_compiler_flag(--ld-path=gold HAVE_GOLD_LINKER_FLAG)
+        check_cxx_compiler_flag(--ld-path=bfd HAVE_BFD_LINKER_FLAG)
+      else()
+        check_cxx_compiler_flag(-fuse-ld=mold HAVE_MOLD_LINKER_FLAG)
+        check_cxx_compiler_flag(-fuse-ld=lld HAVE_LLD_LINKER_FLAG)
+        check_cxx_compiler_flag(-fuse-ld=gold HAVE_GOLD_LINKER_FLAG)
+        check_cxx_compiler_flag(-fuse-ld=bfd HAVE_BFD_LINKER_FLAG)
+      endif()
       find_program(HAVE_MOLD_LINKER_BIN ld.mold)
       find_program(HAVE_LLD_LINKER_BIN lld ld.lld)
       find_program(HAVE_GOLD_LINKER_BIN ld.gold)
@@ -48,7 +55,11 @@ if(ENABLE_TESTING)
       validate_option(CMAKE_CUSTOM_LINKER CMAKE_CUSTOM_LINKER_VALUES)
       mark_as_advanced(CMAKE_CUSTOM_LINKER)
       if(NOT "${CMAKE_CUSTOM_LINKER}" STREQUAL "default")
-        target_link_options(lammps PUBLIC -fuse-ld=${CMAKE_CUSTOM_LINKER})
+        if((CMAKE_CXX_COMPILER_ID STREQUAL "Clang") AND (CMAKE_CXX_COMPILER_VERSION VERSION_GREATER 19.9))
+          target_link_options(lammps PUBLIC --ld-path=${CMAKE_CUSTOM_LINKER})
+        else()
+          target_link_options(lammps PUBLIC -fuse-ld=${CMAKE_CUSTOM_LINKER})
+        endif()
       endif()
     endif()
   endif()

From b3e7121535863df3db487cd3e6a68c080bf2a6b4 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Thu, 15 May 2025 02:13:19 -0400
Subject: [PATCH 03/23] modernize project() command and create project version
 string with dots

---
 cmake/CMakeLists.txt            |  9 ++++++++-
 cmake/Modules/LAMMPSUtils.cmake | 22 +++++++++++++++++-----
 2 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/cmake/CMakeLists.txt b/cmake/CMakeLists.txt
index 67e2e1f327..afa3f2a12e 100644
--- a/cmake/CMakeLists.txt
+++ b/cmake/CMakeLists.txt
@@ -7,6 +7,10 @@ if(CMAKE_VERSION VERSION_LESS 3.20)
   message(WARNING "LAMMPS is planning to require at least CMake version 3.20 by Summer 2025. Please upgrade!")
 endif()
 ########################################
+# initialize version variables with project command
+if(POLICY CMP0048)
+  cmake_policy(SET CMP0048 NEW)
+endif()
 # set policy to silence warnings about ignoring <PackageName>_ROOT but use it
 if(POLICY CMP0074)
   cmake_policy(SET CMP0074 NEW)
@@ -27,7 +31,10 @@ endif()
 
 ########################################
 
-project(lammps CXX)
+project(lammps
+        DESCRIPTION "The LAMMPS Molecular Dynamics Simulator"
+        HOMEPAGE_URL "https://www.lammps.org"
+        LANGUAGES CXX C)
 set(SOVERSION 0)
 get_property(BUILD_IS_MULTI_CONFIG GLOBAL PROPERTY GENERATOR_IS_MULTI_CONFIG)
 
diff --git a/cmake/Modules/LAMMPSUtils.cmake b/cmake/Modules/LAMMPSUtils.cmake
index 4675788647..93f541f921 100644
--- a/cmake/Modules/LAMMPSUtils.cmake
+++ b/cmake/Modules/LAMMPSUtils.cmake
@@ -75,13 +75,25 @@ function(get_lammps_version version_header variable)
     list(FIND MONTHS "${month}" month)
     string(LENGTH ${day} day_length)
     string(LENGTH ${month} month_length)
-    if(day_length EQUAL 1)
-        set(day "0${day}")
+    # no leading zero needed for new version string with dots
+    # if(day_length EQUAL 1)
+    #   set(day "0${day}")
+    # endif()
+    # if(month_length EQUAL 1)
+    #   set(month "0${month}")
+    #endif()
+    file(STRINGS ${version_header} line REGEX LAMMPS_UPDATE)
+    string(REGEX REPLACE "#define LAMMPS_UPDATE \"Update ([0-9]+)\"" "\\1" tweak "${line}")
+    if (line MATCHES "#define LAMMPS_UPDATE \"(Maintenance|Development)\"")
+      set(tweak "99")
     endif()
-    if(month_length EQUAL 1)
-        set(month "0${month}")
+    if(NOT tweak)
+      set(tweak "0")
     endif()
-    set(${variable} "${year}${month}${day}" PARENT_SCOPE)
+    # new version string with dots
+    set(${variable} "${year}.${month}.${day}.${tweak}" PARENT_SCOPE)
+    # old version string without dots
+    # set(${variable} "${year}${month}${day}" PARENT_SCOPE)
 endfunction()
 
 function(check_for_autogen_files source_dir)

From 9abb171d0512ad6655edd6454ee78f4f6e2c0648 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Thu, 15 May 2025 02:49:02 -0400
Subject: [PATCH 04/23] more CMake scripting updates to use C style MPI
 libraries not C++

---
 cmake/CMakeLists.txt                      | 11 ++++-----
 cmake/Modules/MPI4WIN.cmake               | 12 +++++-----
 examples/COUPLE/plugin/CMakeLists.txt     |  2 +-
 examples/COUPLE/simple/CMakeLists.txt     |  4 ++--
 examples/plugins/LAMMPSInterfaceCXX.cmake | 29 ++++++++++++-----------
 5 files changed, 28 insertions(+), 30 deletions(-)

diff --git a/cmake/CMakeLists.txt b/cmake/CMakeLists.txt
index afa3f2a12e..d7f79974de 100644
--- a/cmake/CMakeLists.txt
+++ b/cmake/CMakeLists.txt
@@ -386,7 +386,6 @@ if(PKG_ADIOS)
   # The search for ADIOS2 must come before MPI because
   # it includes its own MPI search with the latest FindMPI.cmake
   # script that defines the MPI::MPI_C target
-  enable_language(C)
   find_package(ADIOS2 REQUIRED)
   if(BUILD_MPI)
     if(NOT ADIOS2_HAVE_MPI)
@@ -401,7 +400,7 @@ if(PKG_ADIOS)
 endif()
 
 if(NOT CMAKE_CROSSCOMPILING)
-  find_package(MPI QUIET)
+  find_package(MPI QUIET COMPONENTS C)
   option(BUILD_MPI "Build MPI version" ${MPI_FOUND})
 else()
   option(BUILD_MPI "Build MPI version" OFF)
@@ -415,7 +414,6 @@ if(BUILD_MPI)
   if((CMAKE_SYSTEM_NAME STREQUAL "Windows") AND CMAKE_CROSSCOMPILING)
     include(MPI4WIN)
   else()
-    enable_language(C)
     find_package(MPI REQUIRED COMPONENTS C)
     option(LAMMPS_LONGLONG_TO_LONG "Workaround if your system or MPI version does not recognize 'long long' data types" OFF)
     if(LAMMPS_LONGLONG_TO_LONG)
@@ -543,7 +541,6 @@ if((CMAKE_CXX_COMPILER_ID STREQUAL "Intel") AND (CMAKE_CXX_STANDARD GREATER_EQUA
 endif()
 
 if(PKG_ATC OR PKG_AWPMD OR PKG_ML-QUIP OR PKG_ML-POD OR PKG_ELECTRODE OR PKG_RHEO OR BUILD_TOOLS)
-  enable_language(C)
   if (NOT USE_INTERNAL_LINALG)
     find_package(LAPACK)
     find_package(BLAS)
@@ -1058,9 +1055,9 @@ else()
 endif()
 if(BUILD_MPI)
   message(STATUS "<<< MPI flags >>>
--- MPI_defines:      ${MPI_CXX_COMPILE_DEFINITIONS}
--- MPI includes:     ${MPI_CXX_INCLUDE_PATH}
--- MPI libraries:    ${MPI_CXX_LIBRARIES};${MPI_Fortran_LIBRARIES}")
+-- MPI_defines:      ${MPI_C_COMPILE_DEFINITIONS}
+-- MPI includes:     ${MPI_C_INCLUDE_PATH}
+-- MPI libraries:    ${MPI_C_LIBRARIES};${MPI_Fortran_LIBRARIES}")
 endif()
 if(PKG_GPU)
   message(STATUS "<<< GPU package settings >>>
diff --git a/cmake/Modules/MPI4WIN.cmake b/cmake/Modules/MPI4WIN.cmake
index 9c5a2c8b6c..18a551b1c7 100644
--- a/cmake/Modules/MPI4WIN.cmake
+++ b/cmake/Modules/MPI4WIN.cmake
@@ -29,9 +29,9 @@ if(USE_MSMPI)
   add_dependencies(MPI::MPI_C mpi4win_build)
 
   # set variables for status reporting at the end of CMake run
-  set(MPI_CXX_INCLUDE_PATH "${SOURCE_DIR}/include")
-  set(MPI_CXX_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
-  set(MPI_CXX_LIBRARIES "${SOURCE_DIR}/lib/libmsmpi.a")
+  set(MPI_C_INCLUDE_PATH "${SOURCE_DIR}/include")
+  set(MPI_C_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
+  set(MPI_C_LIBRARIES "${SOURCE_DIR}/lib/libmsmpi.a")
 else()
   message(STATUS "Downloading and configuring MPICH2-1.4.1 for Windows cross-compilation")
   set(MPICH2_WIN64_DEVEL_URL "${LAMMPS_THIRDPARTY_URL}/mpich2-win64-devel.tar.gz" CACHE STRING "URL for MPICH2 (win64) tarball")
@@ -68,7 +68,7 @@ else()
   add_dependencies(MPI::MPI_C mpi4win_build)
 
   # set variables for status reporting at the end of CMake run
-  set(MPI_CXX_INCLUDE_PATH "${SOURCE_DIR}/include")
-  set(MPI_CXX_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
-  set(MPI_CXX_LIBRARIES "${SOURCE_DIR}/lib/libmpi.a")
+  set(MPI_C_INCLUDE_PATH "${SOURCE_DIR}/include")
+  set(MPI_C_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
+  set(MPI_C_LIBRARIES "${SOURCE_DIR}/lib/libmpi.a")
 endif()
diff --git a/examples/COUPLE/plugin/CMakeLists.txt b/examples/COUPLE/plugin/CMakeLists.txt
index 00f86058fb..c8deb5c7c6 100644
--- a/examples/COUPLE/plugin/CMakeLists.txt
+++ b/examples/COUPLE/plugin/CMakeLists.txt
@@ -27,7 +27,7 @@ if(MSVC)
   add_compile_definitions(_CRT_SECURE_NO_WARNINGS)
 endif()
 
-find_package(MPI REQUIRED)
+find_package(MPI REQUIRED COMPONENTS C)
 # do not include the (obsolete) MPI C++ bindings which makes
 # for leaner object files and avoids namespace conflicts
 set(MPI_CXX_SKIP_MPICXX TRUE)
diff --git a/examples/COUPLE/simple/CMakeLists.txt b/examples/COUPLE/simple/CMakeLists.txt
index c09b372183..6d26db1877 100644
--- a/examples/COUPLE/simple/CMakeLists.txt
+++ b/examples/COUPLE/simple/CMakeLists.txt
@@ -25,7 +25,7 @@ if(MSVC)
   add_compile_definitions(_CRT_SECURE_NO_WARNINGS)
 endif()
 
-find_package(MPI QUIET)
+find_package(MPI QUIET COMPONENTS C)
 # do not include the (obsolete) MPI C++ bindings which makes
 # for leaner object files and avoids namespace conflicts
 set(MPI_CXX_SKIP_MPICXX TRUE)
@@ -38,7 +38,7 @@ if(NOT LAMMPS_SOURCE_DIR)
 endif()
 
 add_executable(simpleCC simple.cpp)
-target_link_libraries(simpleCC PRIVATE LAMMPS::lammps MPI::MPI_CXX)
+target_link_libraries(simpleCC PRIVATE LAMMPS::lammps MPI::MPI_C)
 
 add_executable(simpleC simple.c)
 target_link_libraries(simpleC PRIVATE LAMMPS::lammps MPI::MPI_C)
diff --git a/examples/plugins/LAMMPSInterfaceCXX.cmake b/examples/plugins/LAMMPSInterfaceCXX.cmake
index 4cd4510a61..cdfcb498fe 100644
--- a/examples/plugins/LAMMPSInterfaceCXX.cmake
+++ b/examples/plugins/LAMMPSInterfaceCXX.cmake
@@ -34,8 +34,9 @@ endif()
 ################################################################################
 # MPI configuration
 if(NOT CMAKE_CROSSCOMPILING)
+  enable_language(C)
   set(MPI_CXX_SKIP_MPICXX TRUE)
-  find_package(MPI QUIET)
+  find_package(MPI QUIET COMPONENTS C)
   option(BUILD_MPI "Build MPI version" ${MPI_FOUND})
 else()
   option(BUILD_MPI "Build MPI version" OFF)
@@ -69,17 +70,17 @@ if(BUILD_MPI)
 
       ExternalProject_get_property(mpi4win_build SOURCE_DIR)
       file(MAKE_DIRECTORY "${SOURCE_DIR}/include")
-      add_library(MPI::MPI_CXX UNKNOWN IMPORTED)
-      set_target_properties(MPI::MPI_CXX PROPERTIES
+      add_library(MPI::MPI_C UNKNOWN IMPORTED)
+      set_target_properties(MPI::MPI_C PROPERTIES
         IMPORTED_LOCATION "${SOURCE_DIR}/lib/libmsmpi.a"
         INTERFACE_INCLUDE_DIRECTORIES "${SOURCE_DIR}/include"
         INTERFACE_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
-      add_dependencies(MPI::MPI_CXX mpi4win_build)
+      add_dependencies(MPI::MPI_C mpi4win_build)
 
       # set variables for status reporting at the end of CMake run
-      set(MPI_CXX_INCLUDE_PATH "${SOURCE_DIR}/include")
-      set(MPI_CXX_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
-      set(MPI_CXX_LIBRARIES "${SOURCE_DIR}/lib/libmsmpi.a")
+      set(MPI_C_INCLUDE_PATH "${SOURCE_DIR}/include")
+      set(MPI_C_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
+      set(MPI_C_LIBRARIES "${SOURCE_DIR}/lib/libmsmpi.a")
     else()
       # Download and configure custom MPICH files for Windows
       message(STATUS "Downloading and configuring MPICH-1.4.1 for Windows")
@@ -105,17 +106,17 @@ if(BUILD_MPI)
 
       ExternalProject_get_property(mpi4win_build SOURCE_DIR)
       file(MAKE_DIRECTORY "${SOURCE_DIR}/include")
-      add_library(MPI::MPI_CXX UNKNOWN IMPORTED)
-      set_target_properties(MPI::MPI_CXX PROPERTIES
+      add_library(MPI::MPI_C UNKNOWN IMPORTED)
+      set_target_properties(MPI::MPI_C PROPERTIES
         IMPORTED_LOCATION "${SOURCE_DIR}/lib/libmpi.a"
         INTERFACE_INCLUDE_DIRECTORIES "${SOURCE_DIR}/include"
         INTERFACE_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
-      add_dependencies(MPI::MPI_CXX mpi4win_build)
+      add_dependencies(MPI::MPI_C mpi4win_build)
 
       # set variables for status reporting at the end of CMake run
-      set(MPI_CXX_INCLUDE_PATH "${SOURCE_DIR}/include")
-      set(MPI_CXX_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
-      set(MPI_CXX_LIBRARIES "${SOURCE_DIR}/lib/libmpi.a")
+      set(MPI_C_INCLUDE_PATH "${SOURCE_DIR}/include")
+      set(MPI_C_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
+      set(MPI_C_LIBRARIES "${SOURCE_DIR}/lib/libmpi.a")
     endif()
   else()
     find_package(MPI REQUIRED)
@@ -124,7 +125,7 @@ if(BUILD_MPI)
       target_compile_definitions(lammps INTERFACE -DLAMMPS_LONGLONG_TO_LONG)
     endif()
   endif()
-  target_link_libraries(lammps INTERFACE MPI::MPI_CXX)
+  target_link_libraries(lammps INTERFACE MPI::MPI_C)
 else()
   target_include_directories(lammps INTERFACE "${LAMMPS_SOURCE_DIR}/STUBS")
 endif()

From 2b7c05c057a40fb4c29e658660afbbc2e7d741dc Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Thu, 15 May 2025 04:02:44 -0400
Subject: [PATCH 05/23] properly select linker for modern clang compilers

---
 cmake/Modules/Testing.cmake | 34 +++++++++++++++++-----------------
 1 file changed, 17 insertions(+), 17 deletions(-)

diff --git a/cmake/Modules/Testing.cmake b/cmake/Modules/Testing.cmake
index 4862a0d38e..7aa3506642 100644
--- a/cmake/Modules/Testing.cmake
+++ b/cmake/Modules/Testing.cmake
@@ -21,22 +21,15 @@ if(ENABLE_TESTING)
   # also only verified with Fedora Linux > 30 and Ubuntu 18.04 or 22.04+(Ubuntu 20.04 fails)
   if((CMAKE_SYSTEM_NAME STREQUAL "Linux")
       AND ((CMAKE_CXX_COMPILER_ID STREQUAL "GNU") OR (CMAKE_CXX_COMPILER_ID STREQUAL "Clang")))
-    if(((CMAKE_LINUX_DISTRO STREQUAL "Ubuntu") AND
-          ((CMAKE_DISTRO_VERSION VERSION_LESS_EQUAL 18.04) OR (CMAKE_DISTRO_VERSION VERSION_GREATER_EQUAL 22.04)))
+    if(((CMAKE_LINUX_DISTRO STREQUAL "Ubuntu") AND (CMAKE_DISTRO_VERSION VERSION_GREATER_EQUAL 22.04))
         OR ((CMAKE_LINUX_DISTRO STREQUAL "Fedora") AND (CMAKE_DISTRO_VERSION VERSION_GREATER 30)))
       include(CheckCXXCompilerFlag)
       set(CMAKE_CUSTOM_LINKER_DEFAULT default)
-      if((CMAKE_CXX_COMPILER_ID STREQUAL "Clang") AND (CMAKE_CXX_COMPILER_VERSION VERSION_GREATER 19.9))
-        check_cxx_compiler_flag(--ld-path=mold HAVE_MOLD_LINKER_FLAG)
-        check_cxx_compiler_flag(--ld-path=lld HAVE_LLD_LINKER_FLAG)
-        check_cxx_compiler_flag(--ld-path=gold HAVE_GOLD_LINKER_FLAG)
-        check_cxx_compiler_flag(--ld-path=bfd HAVE_BFD_LINKER_FLAG)
-      else()
-        check_cxx_compiler_flag(-fuse-ld=mold HAVE_MOLD_LINKER_FLAG)
-        check_cxx_compiler_flag(-fuse-ld=lld HAVE_LLD_LINKER_FLAG)
-        check_cxx_compiler_flag(-fuse-ld=gold HAVE_GOLD_LINKER_FLAG)
-        check_cxx_compiler_flag(-fuse-ld=bfd HAVE_BFD_LINKER_FLAG)
-      endif()
+      check_cxx_compiler_flag(--ld-path=${CMAKE_LINKER} HAVE_LD_PATH_FLAG)
+      check_cxx_compiler_flag(-fuse-ld=mold HAVE_MOLD_LINKER_FLAG)
+      check_cxx_compiler_flag(-fuse-ld=lld HAVE_LLD_LINKER_FLAG)
+      check_cxx_compiler_flag(-fuse-ld=gold HAVE_GOLD_LINKER_FLAG)
+      check_cxx_compiler_flag(-fuse-ld=bfd HAVE_BFD_LINKER_FLAG)
       find_program(HAVE_MOLD_LINKER_BIN ld.mold)
       find_program(HAVE_LLD_LINKER_BIN lld ld.lld)
       find_program(HAVE_GOLD_LINKER_BIN ld.gold)
@@ -55,10 +48,17 @@ if(ENABLE_TESTING)
       validate_option(CMAKE_CUSTOM_LINKER CMAKE_CUSTOM_LINKER_VALUES)
       mark_as_advanced(CMAKE_CUSTOM_LINKER)
       if(NOT "${CMAKE_CUSTOM_LINKER}" STREQUAL "default")
-        if((CMAKE_CXX_COMPILER_ID STREQUAL "Clang") AND (CMAKE_CXX_COMPILER_VERSION VERSION_GREATER 19.9))
-          target_link_options(lammps PUBLIC --ld-path=${CMAKE_CUSTOM_LINKER})
-        else()
-          target_link_options(lammps PUBLIC -fuse-ld=${CMAKE_CUSTOM_LINKER})
+        target_link_options(lammps PUBLIC -fuse-ld=${CMAKE_CUSTOM_LINKER})
+      endif()
+      if(HAVE_LD_PATH_FLAG)
+        if("${CMAKE_CUSTOM_LINKER}" STREQUAL "mold")
+          target_link_options(lammps PUBLIC --ld-path=${HAVE_MOLD_LINKER_BIN})
+        elseif("${CMAKE_CUSTOM_LINKER}" STREQUAL "lld")
+          target_link_options(lammps PUBLIC --ld-path=${HAVE_LLD_LINKER_BIN})
+        elseif("${CMAKE_CUSTOM_LINKER}" STREQUAL "gold")
+          target_link_options(lammps PUBLIC --ld-path=${HAVE_GOLD_LINKER_BIN})
+        elseif("${CMAKE_CUSTOM_LINKER}" STREQUAL "bfd")
+          target_link_options(lammps PUBLIC --ld-path=${HAVE_BFD_LINKER_BIN})
         endif()
       endif()
     endif()

From 35f08232ba29dcff99008dad308576fa46633051 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Thu, 15 May 2025 07:46:48 -0400
Subject: [PATCH 06/23] update for Fedora 41/42

---
 cmake/presets/hip_amd.cmake | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/cmake/presets/hip_amd.cmake b/cmake/presets/hip_amd.cmake
index 4b8945e0c7..2cf28c05c4 100644
--- a/cmake/presets/hip_amd.cmake
+++ b/cmake/presets/hip_amd.cmake
@@ -19,12 +19,19 @@ set(CMAKE_C_FLAGS_RELEASE "-O3 -DNDEBUG" CACHE STRING "" FORCE)
 
 set(MPI_CXX "hipcc" CACHE STRING "" FORCE)
 set(MPI_CXX_COMPILER "mpicxx" CACHE STRING "" FORCE)
+set(MPI_C "hipcc" CACHE STRING "" FORCE)
+set(MPI_C_COMPILER "mpicc" CACHE STRING "" FORCE)
+
+# change as needed. This is for Fedora Linux 41 and 42
+set(_libomp_root "/usr/lib/clang/18")
+# we need to explicitly specify the include dir, since hipcc will
+# compile each file twice and doesn't find omp.h the second time
 
 unset(HAVE_OMP_H_INCLUDE CACHE)
 set(OpenMP_C "hipcc" CACHE STRING "" FORCE)
-set(OpenMP_C_FLAGS "-fopenmp" CACHE STRING "" FORCE)
+set(OpenMP_C_FLAGS "-fopenmp=libomp -I${_libomp_root}/include" CACHE STRING "" FORCE)
 set(OpenMP_C_LIB_NAMES "omp" CACHE STRING "" FORCE)
 set(OpenMP_CXX "hipcc" CACHE STRING "" FORCE)
-set(OpenMP_CXX_FLAGS "-fopenmp" CACHE STRING "" FORCE)
+set(OpenMP_CXX_FLAGS "-fopenmp=libomp -I${_libomp_root}/include" CACHE STRING "" FORCE)
 set(OpenMP_CXX_LIB_NAMES "omp" CACHE STRING "" FORCE)
 set(OpenMP_omp_LIBRARY "libomp.so" CACHE PATH "" FORCE)

From fd8fb74a889bc8693625f8ea0b3d917563ad2158 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Thu, 15 May 2025 07:47:19 -0400
Subject: [PATCH 07/23] cannot use Kokkos-OpenMP with recent hipcc

---
 cmake/presets/kokkos-hip.cmake | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/cmake/presets/kokkos-hip.cmake b/cmake/presets/kokkos-hip.cmake
index c1968c0ffa..58b09020fb 100644
--- a/cmake/presets/kokkos-hip.cmake
+++ b/cmake/presets/kokkos-hip.cmake
@@ -1,8 +1,8 @@
-# preset that enables KOKKOS and selects HIP compilation with OpenMP
-# enabled as well. Also sets some performance related compiler flags.
+# preset that enables KOKKOS and selects HIP compilation withOUT OpenMP.
+# Kokkos OpenMP is not compatible with the second pass of hipcc.
 set(PKG_KOKKOS ON CACHE BOOL "" FORCE)
 set(Kokkos_ENABLE_SERIAL ON CACHE BOOL "" FORCE)
-set(Kokkos_ENABLE_OPENMP ON CACHE BOOL "" FORCE)
+set(Kokkos_ENABLE_OPENMP OFF CACHE BOOL "" FORCE)
 set(Kokkos_ENABLE_CUDA   OFF CACHE BOOL "" FORCE)
 set(Kokkos_ENABLE_HIP    ON CACHE BOOL "" FORCE)
 set(Kokkos_ARCH_VEGA90A on CACHE BOOL "" FORCE)
@@ -11,11 +11,11 @@ set(BUILD_OMP ON CACHE BOOL "" FORCE)
 
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -munsafe-fp-atomics" CACHE STRING "" FORCE)
 
-# If KSPACE is also enabled, use CUFFT for FFTs
+# If KSPACE is also enabled, use HIPFFT for FFTs
 set(FFT_KOKKOS "HIPFFT" CACHE STRING "" FORCE)
 
 # hide deprecation warnings temporarily for stable release
-set(Kokkos_ENABLE_DEPRECATION_WARNINGS OFF CACHE BOOL "" FORCE)
+#set(Kokkos_ENABLE_DEPRECATION_WARNINGS OFF CACHE BOOL "" FORCE)
 
 # these flags are needed to build with Cray MPICH on OLCF Crusher
 #-D CMAKE_CXX_FLAGS="-I/${MPICH_DIR}/include"

From 5a8da735f26c94e3b9a06274f388036525ac79a1 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Mon, 19 May 2025 21:14:33 -0400
Subject: [PATCH 08/23] explicitly use the MPI::C imported target on the main
 executable

---
 cmake/CMakeLists.txt | 1 +
 1 file changed, 1 insertion(+)

diff --git a/cmake/CMakeLists.txt b/cmake/CMakeLists.txt
index d7f79974de..3568095d4d 100644
--- a/cmake/CMakeLists.txt
+++ b/cmake/CMakeLists.txt
@@ -421,6 +421,7 @@ if(BUILD_MPI)
     endif()
   endif()
   target_link_libraries(lammps PUBLIC MPI::MPI_C)
+  target_link_libraries(lmp PUBLIC MPI::MPI_C)
 else()
   target_sources(lammps PRIVATE ${LAMMPS_SOURCE_DIR}/STUBS/mpi.cpp)
   add_library(mpi_stubs INTERFACE)

From 09b174d129e6b1596e75a08cf9be67601ea7e271 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Mon, 19 May 2025 21:15:00 -0400
Subject: [PATCH 09/23] turn off C++ support

---
 unittest/c-library/CMakeLists.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/unittest/c-library/CMakeLists.txt b/unittest/c-library/CMakeLists.txt
index 62ec750a3f..5b5dd4f357 100644
--- a/unittest/c-library/CMakeLists.txt
+++ b/unittest/c-library/CMakeLists.txt
@@ -70,7 +70,7 @@ add_test(NAME LibraryConfig COMMAND test_library_config)
 
 add_executable(test_library_mpi test_library_mpi.cpp)
 target_link_libraries(test_library_mpi PRIVATE lammps GTest::GMock)
-target_compile_definitions(test_library_mpi PRIVATE ${TEST_CONFIG_DEFS})
+target_compile_definitions(test_library_mpi PRIVATE "${TEST_CONFIG_DEFS};MPICH_SKIP_MPICXX;OMPI_SKIP_MPICXX=1")
 add_mpi_test(NAME LibraryMPI NUM_PROCS 4 COMMAND $<TARGET_FILE:test_library_mpi>)
 
 # simple run tests for coupling to the LAMMPS library

From 186a6431f7a074fc7b1d5528d207ff299269b0c3 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Mon, 19 May 2025 21:27:57 -0400
Subject: [PATCH 10/23] directly disable C++ support when compiling main.cpp

---
 cmake/CMakeLists.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/cmake/CMakeLists.txt b/cmake/CMakeLists.txt
index 3568095d4d..1c79fef956 100644
--- a/cmake/CMakeLists.txt
+++ b/cmake/CMakeLists.txt
@@ -421,7 +421,7 @@ if(BUILD_MPI)
     endif()
   endif()
   target_link_libraries(lammps PUBLIC MPI::MPI_C)
-  target_link_libraries(lmp PUBLIC MPI::MPI_C)
+  target_compile_definitions(lmp PRIVATE -DMPICH_SKIP_MPICXX -DOMPI_SKIP_MPICXX=1)
 else()
   target_sources(lammps PRIVATE ${LAMMPS_SOURCE_DIR}/STUBS/mpi.cpp)
   add_library(mpi_stubs INTERFACE)

From 70e1bb50f182fc4acb328588d97a3502c0e4d014 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Mon, 19 May 2025 21:40:44 -0400
Subject: [PATCH 11/23] add skip C++ defines for LAMMPS library instead

---
 cmake/CMakeLists.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/cmake/CMakeLists.txt b/cmake/CMakeLists.txt
index 1c79fef956..1d3ddc04da 100644
--- a/cmake/CMakeLists.txt
+++ b/cmake/CMakeLists.txt
@@ -421,7 +421,7 @@ if(BUILD_MPI)
     endif()
   endif()
   target_link_libraries(lammps PUBLIC MPI::MPI_C)
-  target_compile_definitions(lmp PRIVATE -DMPICH_SKIP_MPICXX -DOMPI_SKIP_MPICXX=1)
+  target_compile_definitions(lammps PUBLIC -DMPICH_SKIP_MPICXX -DOMPI_SKIP_MPICXX=1)
 else()
   target_sources(lammps PRIVATE ${LAMMPS_SOURCE_DIR}/STUBS/mpi.cpp)
   add_library(mpi_stubs INTERFACE)

From 510563f5f3832cb5fd49b49cdc015ea62b76f95f Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Mon, 19 May 2025 21:51:53 -0400
Subject: [PATCH 12/23] explicitly skip MPI C++ interface in colvars

---
 cmake/Modules/Packages/COLVARS.cmake | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/cmake/Modules/Packages/COLVARS.cmake b/cmake/Modules/Packages/COLVARS.cmake
index 55fbc52abf..7b21c5804e 100644
--- a/cmake/Modules/Packages/COLVARS.cmake
+++ b/cmake/Modules/Packages/COLVARS.cmake
@@ -27,7 +27,7 @@ if(BUILD_OMP)
 endif()
 
 if(BUILD_MPI)
-  target_compile_definitions(colvars PUBLIC -DCOLVARS_MPI)
+  target_compile_definitions(colvars PUBLIC -DCOLVARS_MPI -DMPICH_SKIP_MPICXX -DOMPI_SKIP_MPICXX=1)
   target_link_libraries(colvars PUBLIC MPI::MPI_C)
 endif()
 

From 2cc1356384b5aba182f610a01462f0c1d9a4da4b Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Mon, 19 May 2025 22:09:38 -0400
Subject: [PATCH 13/23] skip MPI C++ support also for libraries

---
 cmake/CMakeLists.txt | 1 +
 1 file changed, 1 insertion(+)

diff --git a/cmake/CMakeLists.txt b/cmake/CMakeLists.txt
index 1d3ddc04da..b75dc92b63 100644
--- a/cmake/CMakeLists.txt
+++ b/cmake/CMakeLists.txt
@@ -717,6 +717,7 @@ foreach(PKG_LIB POEMS ATC AWPMD H5MD)
     file(GLOB_RECURSE ${PKG_LIB}_SOURCES CONFIGURE_DEPENDS
       ${LAMMPS_LIB_SOURCE_DIR}/${PKG_LIB}/[^.]*.c ${LAMMPS_LIB_SOURCE_DIR}/${PKG_LIB}/[^.]*.cpp)
     add_library(${PKG_LIB} STATIC ${${PKG_LIB}_SOURCES})
+    target_compile_definitions(${PKG_LIB} PUBLIC -DMPICH_SKIP_MPICXX -DOMPI_SKIP_MPICXX=1)
     set_target_properties(${PKG_LIB} PROPERTIES OUTPUT_NAME lammps_${PKG_LIB}${LAMMPS_MACHINE})
     target_link_libraries(lammps PRIVATE ${PKG_LIB})
     if(PKG_LIB STREQUAL "awpmd")

From adce5bef84caf48044f058b9853681e3a3b19759 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Mon, 19 May 2025 22:20:50 -0400
Subject: [PATCH 14/23] explicitly skip MPI C++ in GPU package library

---
 cmake/Modules/Packages/GPU.cmake | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/cmake/Modules/Packages/GPU.cmake b/cmake/Modules/Packages/GPU.cmake
index f32e97c3eb..4c4ace1abd 100644
--- a/cmake/Modules/Packages/GPU.cmake
+++ b/cmake/Modules/Packages/GPU.cmake
@@ -489,7 +489,7 @@ else()
   target_link_libraries(gpu PRIVATE mpi_stubs)
 endif()
 
-target_compile_definitions(gpu PRIVATE -DLAMMPS_${LAMMPS_SIZES})
+target_compile_definitions(gpu PRIVATE -DLAMMPS_${LAMMPS_SIZES} -DMPICH_SKIP_MPICXX -DOMPI_SKIP_MPICXX=1)
 set_target_properties(gpu PROPERTIES OUTPUT_NAME lammps_gpu${LAMMPS_MACHINE})
 target_sources(lammps PRIVATE ${GPU_SOURCES})
 target_include_directories(lammps PRIVATE ${GPU_SOURCES_DIR})

From 271bdc1af73fc14335e2442d6d3dbd707b72698b Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Tue, 20 May 2025 13:56:36 -0400
Subject: [PATCH 15/23] alternate way to specify defines for MPI tests

---
 unittest/c-library/CMakeLists.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/unittest/c-library/CMakeLists.txt b/unittest/c-library/CMakeLists.txt
index 5b5dd4f357..142c4d3523 100644
--- a/unittest/c-library/CMakeLists.txt
+++ b/unittest/c-library/CMakeLists.txt
@@ -70,7 +70,7 @@ add_test(NAME LibraryConfig COMMAND test_library_config)
 
 add_executable(test_library_mpi test_library_mpi.cpp)
 target_link_libraries(test_library_mpi PRIVATE lammps GTest::GMock)
-target_compile_definitions(test_library_mpi PRIVATE "${TEST_CONFIG_DEFS};MPICH_SKIP_MPICXX;OMPI_SKIP_MPICXX=1")
+target_compile_definitions(test_library_mpi PRIVATE "${TEST_CONFIG_DEFS};-DMPICH_SKIP_MPICXX;-DOMPI_SKIP_MPICXX=1")
 add_mpi_test(NAME LibraryMPI NUM_PROCS 4 COMMAND $<TARGET_FILE:test_library_mpi>)
 
 # simple run tests for coupling to the LAMMPS library

From 35528479576faa04361d4ba68ccaeb3eedf083a2 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Wed, 28 May 2025 21:35:33 -0400
Subject: [PATCH 16/23] consistent use of definitions to avoid CMake adding
 spurious '-D' prefixes

---
 unittest/c-library/CMakeLists.txt | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/unittest/c-library/CMakeLists.txt b/unittest/c-library/CMakeLists.txt
index 5b5dd4f357..240da8bcf3 100644
--- a/unittest/c-library/CMakeLists.txt
+++ b/unittest/c-library/CMakeLists.txt
@@ -31,28 +31,28 @@ target_compile_definitions(test_library_scatter_gather PRIVATE -DTEST_INPUT_FOLD
 add_test(NAME LibraryScatterGather COMMAND test_library_scatter_gather)
 set_tests_properties(LibraryScatterGather PROPERTIES ENVIRONMENT "LAMMPS_POTENTIALS=${LAMMPS_POTENTIALS_DIR}")
 
-set(TEST_CONFIG_DEFS "-DTEST_INPUT_FOLDER=${CMAKE_CURRENT_SOURCE_DIR};-DLAMMPS_${LAMMPS_SIZES}")
+set(TEST_CONFIG_DEFS "TEST_INPUT_FOLDER=${CMAKE_CURRENT_SOURCE_DIR};LAMMPS_${LAMMPS_SIZES}")
 set(PKG_COUNT 0)
 foreach(PKG ${STANDARD_PACKAGES} ${EXTRA_PACKAGES} ${SUFFIX_PACKAGES})
   if(PKG_${PKG})
     MATH(EXPR PKG_COUNT "${PKG_COUNT}+1")
   endif()
 endforeach()
-list(APPEND TEST_CONFIG_DEFS -DNUM_LAMMPS_PACKAGES=${PKG_COUNT})
+list(APPEND TEST_CONFIG_DEFS NUM_LAMMPS_PACKAGES=${PKG_COUNT})
 
 if(PKG_MANYBODY)
   set(HAS_MANYBODY 1)
 else()
   set(HAS_MANYBODY 0)
 endif()
-list(APPEND TEST_CONFIG_DEFS -DLAMMPS_HAS_MANYBODY=${HAS_MANYBODY})
+list(APPEND TEST_CONFIG_DEFS LAMMPS_HAS_MANYBODY=${HAS_MANYBODY})
 
 if(BUILD_MPI)
   set(HAS_MPI 1)
 else()
   set(HAS_MPI 0)
 endif()
-list(APPEND TEST_CONFIG_DEFS -DLAMMPS_HAS_MPI=${HAS_MPI})
+list(APPEND TEST_CONFIG_DEFS LAMMPS_HAS_MPI=${HAS_MPI})
 
 foreach(WITH "JPEG" "PNG" "GZIP" "FFMPEG")
   if(WITH_${WITH})
@@ -60,7 +60,7 @@ foreach(WITH "JPEG" "PNG" "GZIP" "FFMPEG")
   else()
     set(HAS_${WITH} 0)
   endif()
-  list(APPEND TEST_CONFIG_DEFS -DLAMMPS_HAS_${WITH}=${HAS_${WITH}})
+  list(APPEND TEST_CONFIG_DEFS LAMMPS_HAS_${WITH}=${HAS_${WITH}})
 endforeach()
 
 add_executable(test_library_config test_library_config.cpp test_main.cpp)

From be59eb6a703361f1cbce51bc53b51d670f61d475 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Wed, 28 May 2025 21:38:14 -0400
Subject: [PATCH 17/23] fix up two more inconsistent definitions

---
 unittest/c-library/CMakeLists.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/unittest/c-library/CMakeLists.txt b/unittest/c-library/CMakeLists.txt
index 811f7e2729..169aea91df 100644
--- a/unittest/c-library/CMakeLists.txt
+++ b/unittest/c-library/CMakeLists.txt
@@ -70,7 +70,7 @@ add_test(NAME LibraryConfig COMMAND test_library_config)
 
 add_executable(test_library_mpi test_library_mpi.cpp)
 target_link_libraries(test_library_mpi PRIVATE lammps GTest::GMock)
-target_compile_definitions(test_library_mpi PRIVATE "${TEST_CONFIG_DEFS};-DMPICH_SKIP_MPICXX;-DOMPI_SKIP_MPICXX=1")
+target_compile_definitions(test_library_mpi PRIVATE "${TEST_CONFIG_DEFS};MPICH_SKIP_MPICXX=1;OMPI_SKIP_MPICXX=1")
 add_mpi_test(NAME LibraryMPI NUM_PROCS 4 COMMAND $<TARGET_FILE:test_library_mpi>)
 
 # simple run tests for coupling to the LAMMPS library

From 1fae7e3f9839a635e2b7aa36c97e850e02d4cce3 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Mon, 2 Jun 2025 15:47:35 -0400
Subject: [PATCH 18/23] remove support for obsolete MPICH library binaries for
 Windows

---
 cmake/Modules/LAMMPSInterfacePlugin.cmake | 98 +++++++---------------
 cmake/Modules/MPI4WIN.cmake               | 99 +++++++----------------
 examples/plugins/LAMMPSInterfaceCXX.cmake | 99 +++++++----------------
 3 files changed, 85 insertions(+), 211 deletions(-)

diff --git a/cmake/Modules/LAMMPSInterfacePlugin.cmake b/cmake/Modules/LAMMPSInterfacePlugin.cmake
index 2363937af5..7c71c6dae2 100644
--- a/cmake/Modules/LAMMPSInterfacePlugin.cmake
+++ b/cmake/Modules/LAMMPSInterfacePlugin.cmake
@@ -142,84 +142,44 @@ if(BUILD_MPI)
   set(MPI_CXX_SKIP_MPICXX TRUE)
   # We use a non-standard procedure to cross-compile with MPI on Windows
   if((CMAKE_SYSTEM_NAME STREQUAL "Windows") AND CMAKE_CROSSCOMPILING)
-    # Download and configure MinGW compatible MPICH development files for Windows
-    option(USE_MSMPI "Use Microsoft's MS-MPI SDK instead of MPICH2-1.4.1" OFF)
-    if(USE_MSMPI)
-      message(STATUS "Downloading and configuring MS-MPI 10.1 for Windows cross-compilation")
-      set(MPICH2_WIN64_DEVEL_URL "${LAMMPS_THIRDPARTY_URL}/msmpi-win64-devel.tar.gz" CACHE STRING "URL for MS-MPI (win64) tarball")
-      set(MPICH2_WIN64_DEVEL_MD5 "86314daf1bffb809f1fcbefb8a547490" CACHE STRING "MD5 checksum of MS-MPI (win64) tarball")
-      mark_as_advanced(MPICH2_WIN64_DEVEL_URL)
-      mark_as_advanced(MPICH2_WIN64_DEVEL_MD5)
+    message(STATUS "Downloading and configuring MS-MPI 10.1 for Windows cross-compilation")
+    set(MPICH2_WIN64_DEVEL_URL "${LAMMPS_THIRDPARTY_URL}/msmpi-win64-devel.tar.gz" CACHE STRING "URL for MS-MPI (win64) tarball")
+    set(MPICH2_WIN64_DEVEL_MD5 "86314daf1bffb809f1fcbefb8a547490" CACHE STRING "MD5 checksum of MS-MPI (win64) tarball")
+    mark_as_advanced(MPICH2_WIN64_DEVEL_URL)
+    mark_as_advanced(MPICH2_WIN64_DEVEL_MD5)
 
-      include(ExternalProject)
-      if(CMAKE_SYSTEM_PROCESSOR STREQUAL "x86_64")
-        ExternalProject_Add(mpi4win_build
-          URL     ${MPICH2_WIN64_DEVEL_URL}
-          URL_MD5 ${MPICH2_WIN64_DEVEL_MD5}
-          CONFIGURE_COMMAND "" BUILD_COMMAND "" INSTALL_COMMAND ""
-          BUILD_BYPRODUCTS <SOURCE_DIR>/lib/libmsmpi.a)
-      else()
-        message(FATAL_ERROR "Only x86 64-bit builds are supported with MS-MPI")
-      endif()
-
-      ExternalProject_get_property(mpi4win_build SOURCE_DIR)
-      file(MAKE_DIRECTORY "${SOURCE_DIR}/include")
-      add_library(MPI::MPI_C UNKNOWN IMPORTED)
-      set_target_properties(MPI::MPI_C PROPERTIES
-        IMPORTED_LOCATION "${SOURCE_DIR}/lib/libmsmpi.a"
-        INTERFACE_INCLUDE_DIRECTORIES "${SOURCE_DIR}/include"
-        INTERFACE_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
-      add_dependencies(MPI::MPI_C mpi4win_build)
-
-      # set variables for status reporting at the end of CMake run
-      set(MPI_CXX_INCLUDE_PATH "${SOURCE_DIR}/include")
-      set(MPI_CXX_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
-      set(MPI_CXX_LIBRARIES "${SOURCE_DIR}/lib/libmsmpi.a")
+    include(ExternalProject)
+    if(CMAKE_SYSTEM_PROCESSOR STREQUAL "x86_64")
+      ExternalProject_Add(mpi4win_build
+        URL     ${MPICH2_WIN64_DEVEL_URL}
+        URL_MD5 ${MPICH2_WIN64_DEVEL_MD5}
+        CONFIGURE_COMMAND "" BUILD_COMMAND "" INSTALL_COMMAND ""
+        BUILD_BYPRODUCTS <SOURCE_DIR>/lib/libmsmpi.a)
     else()
-      # Download and configure custom MPICH files for Windows
-      message(STATUS "Downloading and configuring MPICH-1.4.1 for Windows")
-      set(MPICH2_WIN64_DEVEL_URL "${LAMMPS_THIRDPARTY_URL}/mpich2-win64-devel.tar.gz" CACHE STRING "URL for MPICH2 (win64) tarball")
-      set(MPICH2_WIN64_DEVEL_MD5 "4939fdb59d13182fd5dd65211e469f14" CACHE STRING "MD5 checksum of MPICH2 (win64) tarball")
-      mark_as_advanced(MPICH2_WIN64_DEVEL_URL)
-      mark_as_advanced(MPICH2_WIN64_DEVEL_MD5)
-
-      include(ExternalProject)
-      if(CMAKE_SYSTEM_PROCESSOR STREQUAL "x86_64")
-        ExternalProject_Add(mpi4win_build
-          URL     ${MPICH2_WIN64_DEVEL_URL}
-          URL_MD5 ${MPICH2_WIN64_DEVEL_MD5}
-          CONFIGURE_COMMAND "" BUILD_COMMAND "" INSTALL_COMMAND ""
-          BUILD_BYPRODUCTS <SOURCE_DIR>/lib/libmpi.a)
-      else()
-        ExternalProject_Add(mpi4win_build
-          URL     ${MPICH2_WIN32_DEVEL_URL}
-          URL_MD5 ${MPICH2_WIN32_DEVEL_MD5}
-          CONFIGURE_COMMAND "" BUILD_COMMAND "" INSTALL_COMMAND ""
-          BUILD_BYPRODUCTS <SOURCE_DIR>/lib/libmpi.a)
-      endif()
-
-      ExternalProject_get_property(mpi4win_build SOURCE_DIR)
-      file(MAKE_DIRECTORY "${SOURCE_DIR}/include")
-      add_library(MPI::MPI_C UNKNOWN IMPORTED)
-      set_target_properties(MPI::MPI_C PROPERTIES
-        IMPORTED_LOCATION "${SOURCE_DIR}/lib/libmpi.a"
-        INTERFACE_INCLUDE_DIRECTORIES "${SOURCE_DIR}/include"
-        INTERFACE_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
-      add_dependencies(MPI::MPI_C mpi4win_build)
-
-      # set variables for status reporting at the end of CMake run
-      set(MPI_CXX_INCLUDE_PATH "${SOURCE_DIR}/include")
-      set(MPI_CXX_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
-      set(MPI_CXX_LIBRARIES "${SOURCE_DIR}/lib/libmpi.a")
+      message(FATAL_ERROR "Only x86 64-bit builds are supported with MS-MPI")
     endif()
+
+    ExternalProject_get_property(mpi4win_build SOURCE_DIR)
+    file(MAKE_DIRECTORY "${SOURCE_DIR}/include")
+    add_library(MPI::MPI_CXX UNKNOWN IMPORTED)
+    set_target_properties(MPI::MPI_CXX PROPERTIES
+      IMPORTED_LOCATION "${SOURCE_DIR}/lib/libmsmpi.a"
+      INTERFACE_INCLUDE_DIRECTORIES "${SOURCE_DIR}/include"
+      INTERFACE_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX=1")
+    add_dependencies(MPI::MPI_CXX mpi4win_build)
+
+    # set variables for status reporting at the end of CMake run
+    set(MPI_CXX_INCLUDE_PATH "${SOURCE_DIR}/include")
+    set(MPI_CXX_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX=1")
+    set(MPI_CXX_LIBRARIES "${SOURCE_DIR}/lib/libmsmpi.a")
   else()
-    find_package(MPI REQUIRED COMPONENTS C)
+    find_package(MPI REQUIRED COMPONENTS CXX)
     option(LAMMPS_LONGLONG_TO_LONG "Workaround if your system or MPI version does not recognize 'long long' data types" OFF)
     if(LAMMPS_LONGLONG_TO_LONG)
       target_compile_definitions(lammps INTERFACE -DLAMMPS_LONGLONG_TO_LONG)
     endif()
   endif()
-  target_link_libraries(lammps INTERFACE MPI::MPI_C)
+  target_link_libraries(lammps INTERFACE MPI::MPI_CXX)
 else()
   add_library(mpi_stubs INTERFACE)
   target_include_directories(mpi_stubs INTERFACE $<BUILD_INTERFACE:${LAMMPS_SOURCE_DIR}/STUBS>)
diff --git a/cmake/Modules/MPI4WIN.cmake b/cmake/Modules/MPI4WIN.cmake
index 18a551b1c7..b5e60616ea 100644
--- a/cmake/Modules/MPI4WIN.cmake
+++ b/cmake/Modules/MPI4WIN.cmake
@@ -1,74 +1,31 @@
-# Download and configure MinGW compatible MPICH development files for Windows
-option(USE_MSMPI "Use Microsoft's MS-MPI SDK instead of MPICH2-1.4.1" OFF)
+# set-up MS-MPI library for Windows with MinGW compatibility
+message(STATUS "Downloading and configuring MS-MPI 10.1 for Windows cross-compilation")
+set(MPICH2_WIN64_DEVEL_URL "${LAMMPS_THIRDPARTY_URL}/msmpi-win64-devel.tar.gz" CACHE STRING "URL for MS-MPI (win64) tarball")
+set(MPICH2_WIN64_DEVEL_MD5 "86314daf1bffb809f1fcbefb8a547490" CACHE STRING "MD5 checksum of MS-MPI (win64) tarball")
+mark_as_advanced(MPICH2_WIN64_DEVEL_URL)
+mark_as_advanced(MPICH2_WIN64_DEVEL_MD5)
 
-if(USE_MSMPI)
-  message(STATUS "Downloading and configuring MS-MPI 10.1 for Windows cross-compilation")
-  set(MPICH2_WIN64_DEVEL_URL "${LAMMPS_THIRDPARTY_URL}/msmpi-win64-devel.tar.gz" CACHE STRING "URL for MS-MPI (win64) tarball")
-  set(MPICH2_WIN64_DEVEL_MD5 "86314daf1bffb809f1fcbefb8a547490" CACHE STRING "MD5 checksum of MS-MPI (win64) tarball")
-  mark_as_advanced(MPICH2_WIN64_DEVEL_URL)
-  mark_as_advanced(MPICH2_WIN64_DEVEL_MD5)
-
-  include(ExternalProject)
-  if(CMAKE_SYSTEM_PROCESSOR STREQUAL "x86_64")
-    ExternalProject_Add(mpi4win_build
-      URL     ${MPICH2_WIN64_DEVEL_URL}
-      URL_MD5 ${MPICH2_WIN64_DEVEL_MD5}
-      CONFIGURE_COMMAND "" BUILD_COMMAND "" INSTALL_COMMAND ""
-      BUILD_BYPRODUCTS <SOURCE_DIR>/lib/libmsmpi.a)
-  else()
-    message(FATAL_ERROR "Only x86 64-bit builds are supported with MS-MPI")
-  endif()
-
-  ExternalProject_get_property(mpi4win_build SOURCE_DIR)
-  file(MAKE_DIRECTORY "${SOURCE_DIR}/include")
-  add_library(MPI::MPI_C UNKNOWN IMPORTED)
-  set_target_properties(MPI::MPI_C PROPERTIES
-    IMPORTED_LOCATION "${SOURCE_DIR}/lib/libmsmpi.a"
-    INTERFACE_INCLUDE_DIRECTORIES "${SOURCE_DIR}/include"
-    INTERFACE_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
-  add_dependencies(MPI::MPI_C mpi4win_build)
-
-  # set variables for status reporting at the end of CMake run
-  set(MPI_C_INCLUDE_PATH "${SOURCE_DIR}/include")
-  set(MPI_C_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
-  set(MPI_C_LIBRARIES "${SOURCE_DIR}/lib/libmsmpi.a")
+include(ExternalProject)
+if(CMAKE_SYSTEM_PROCESSOR STREQUAL "x86_64")
+  ExternalProject_Add(mpi4win_build
+    URL     ${MPICH2_WIN64_DEVEL_URL}
+    URL_MD5 ${MPICH2_WIN64_DEVEL_MD5}
+    CONFIGURE_COMMAND "" BUILD_COMMAND "" INSTALL_COMMAND ""
+    BUILD_BYPRODUCTS <SOURCE_DIR>/lib/libmsmpi.a)
 else()
-  message(STATUS "Downloading and configuring MPICH2-1.4.1 for Windows cross-compilation")
-  set(MPICH2_WIN64_DEVEL_URL "${LAMMPS_THIRDPARTY_URL}/mpich2-win64-devel.tar.gz" CACHE STRING "URL for MPICH2 (win64) tarball")
-  set(MPICH2_WIN32_DEVEL_URL "${LAMMPS_THIRDPARTY_URL}/mpich2-win32-devel.tar.gz" CACHE STRING "URL for MPICH2 (win32) tarball")
-  set(MPICH2_WIN64_DEVEL_MD5 "4939fdb59d13182fd5dd65211e469f14" CACHE STRING "MD5 checksum of MPICH2 (win64) tarball")
-  set(MPICH2_WIN32_DEVEL_MD5 "a61d153500dce44e21b755ee7257e031" CACHE STRING "MD5 checksum of MPICH2 (win32) tarball")
-  mark_as_advanced(MPICH2_WIN64_DEVEL_URL)
-  mark_as_advanced(MPICH2_WIN32_DEVEL_URL)
-  mark_as_advanced(MPICH2_WIN64_DEVEL_MD5)
-  mark_as_advanced(MPICH2_WIN32_DEVEL_MD5)
-
-  include(ExternalProject)
-  if(CMAKE_SYSTEM_PROCESSOR STREQUAL "x86_64")
-    ExternalProject_Add(mpi4win_build
-      URL     ${MPICH2_WIN64_DEVEL_URL}
-      URL_MD5 ${MPICH2_WIN64_DEVEL_MD5}
-      CONFIGURE_COMMAND "" BUILD_COMMAND "" INSTALL_COMMAND ""
-      BUILD_BYPRODUCTS <SOURCE_DIR>/lib/libmpi.a)
-  else()
-    ExternalProject_Add(mpi4win_build
-      URL     ${MPICH2_WIN32_DEVEL_URL}
-      URL_MD5 ${MPICH2_WIN32_DEVEL_MD5}
-      CONFIGURE_COMMAND "" BUILD_COMMAND "" INSTALL_COMMAND ""
-      BUILD_BYPRODUCTS <SOURCE_DIR>/lib/libmpi.a)
-  endif()
-
-  ExternalProject_get_property(mpi4win_build SOURCE_DIR)
-  file(MAKE_DIRECTORY "${SOURCE_DIR}/include")
-  add_library(MPI::MPI_C UNKNOWN IMPORTED)
-  set_target_properties(MPI::MPI_C PROPERTIES
-    IMPORTED_LOCATION "${SOURCE_DIR}/lib/libmpi.a"
-    INTERFACE_INCLUDE_DIRECTORIES "${SOURCE_DIR}/include"
-    INTERFACE_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
-  add_dependencies(MPI::MPI_C mpi4win_build)
-
-  # set variables for status reporting at the end of CMake run
-  set(MPI_C_INCLUDE_PATH "${SOURCE_DIR}/include")
-  set(MPI_C_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
-  set(MPI_C_LIBRARIES "${SOURCE_DIR}/lib/libmpi.a")
+  message(FATAL_ERROR "Only x86 64-bit builds are supported with MS-MPI")
 endif()
+
+ExternalProject_get_property(mpi4win_build SOURCE_DIR)
+file(MAKE_DIRECTORY "${SOURCE_DIR}/include")
+add_library(MPI::MPI_C UNKNOWN IMPORTED)
+set_target_properties(MPI::MPI_CXXx PROPERTIES
+  IMPORTED_LOCATION "${SOURCE_DIR}/lib/libmsmpi.a"
+  INTERFACE_INCLUDE_DIRECTORIES "${SOURCE_DIR}/include"
+  INTERFACE_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX=1")
+add_dependencies(MPI::MPI_CXX mpi4win_build)
+
+# set variables for status reporting at the end of CMake run
+set(MPI_CXX_INCLUDE_PATH "${SOURCE_DIR}/include")
+set(MPI_CXX_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX=1")
+set(MPI_CXX_LIBRARIES "${SOURCE_DIR}/lib/libmsmpi.a")
diff --git a/examples/plugins/LAMMPSInterfaceCXX.cmake b/examples/plugins/LAMMPSInterfaceCXX.cmake
index cdfcb498fe..207b579c89 100644
--- a/examples/plugins/LAMMPSInterfaceCXX.cmake
+++ b/examples/plugins/LAMMPSInterfaceCXX.cmake
@@ -43,81 +43,38 @@ else()
 endif()
 
 if(BUILD_MPI)
-  # do not include the (obsolete) MPI C++ bindings which makes
-  # for leaner object files and avoids namespace conflicts
-  set(MPI_CXX_SKIP_MPICXX TRUE)
   # We use a non-standard procedure to cross-compile with MPI on Windows
   if((CMAKE_SYSTEM_NAME STREQUAL "Windows") AND CMAKE_CROSSCOMPILING)
-    # Download and configure MinGW compatible MPICH development files for Windows
-    option(USE_MSMPI "Use Microsoft's MS-MPI SDK instead of MPICH2-1.4.1" OFF)
-    if(USE_MSMPI)
-      message(STATUS "Downloading and configuring MS-MPI 10.1 for Windows cross-compilation")
-      set(MPICH2_WIN64_DEVEL_URL "${LAMMPS_THIRDPARTY_URL}/msmpi-win64-devel.tar.gz" CACHE STRING "URL for MS-MPI (win64) tarball")
-      set(MPICH2_WIN64_DEVEL_MD5 "86314daf1bffb809f1fcbefb8a547490" CACHE STRING "MD5 checksum of MS-MPI (win64) tarball")
-      mark_as_advanced(MPICH2_WIN64_DEVEL_URL)
-      mark_as_advanced(MPICH2_WIN64_DEVEL_MD5)
+    message(STATUS "Downloading and configuring MS-MPI 10.1 for Windows cross-compilation")
+    set(MPICH2_WIN64_DEVEL_URL "${LAMMPS_THIRDPARTY_URL}/msmpi-win64-devel.tar.gz" CACHE STRING "URL for MS-MPI (win64) tarball")
+    set(MPICH2_WIN64_DEVEL_MD5 "86314daf1bffb809f1fcbefb8a547490" CACHE STRING "MD5 checksum of MS-MPI (win64) tarball")
+    mark_as_advanced(MPICH2_WIN64_DEVEL_URL)
+    mark_as_advanced(MPICH2_WIN64_DEVEL_MD5)
 
-      include(ExternalProject)
-      if(CMAKE_SYSTEM_PROCESSOR STREQUAL "x86_64")
-        ExternalProject_Add(mpi4win_build
-          URL     ${MPICH2_WIN64_DEVEL_URL}
-          URL_MD5 ${MPICH2_WIN64_DEVEL_MD5}
-          CONFIGURE_COMMAND "" BUILD_COMMAND "" INSTALL_COMMAND ""
-          BUILD_BYPRODUCTS <SOURCE_DIR>/lib/libmsmpi.a)
-      else()
-        message(FATAL_ERROR "Only x86 64-bit builds are supported with MS-MPI")
-      endif()
-
-      ExternalProject_get_property(mpi4win_build SOURCE_DIR)
-      file(MAKE_DIRECTORY "${SOURCE_DIR}/include")
-      add_library(MPI::MPI_C UNKNOWN IMPORTED)
-      set_target_properties(MPI::MPI_C PROPERTIES
-        IMPORTED_LOCATION "${SOURCE_DIR}/lib/libmsmpi.a"
-        INTERFACE_INCLUDE_DIRECTORIES "${SOURCE_DIR}/include"
-        INTERFACE_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
-      add_dependencies(MPI::MPI_C mpi4win_build)
-
-      # set variables for status reporting at the end of CMake run
-      set(MPI_C_INCLUDE_PATH "${SOURCE_DIR}/include")
-      set(MPI_C_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
-      set(MPI_C_LIBRARIES "${SOURCE_DIR}/lib/libmsmpi.a")
+    include(ExternalProject)
+    if(CMAKE_SYSTEM_PROCESSOR STREQUAL "x86_64")
+      ExternalProject_Add(mpi4win_build
+        URL     ${MPICH2_WIN64_DEVEL_URL}
+        URL_MD5 ${MPICH2_WIN64_DEVEL_MD5}
+        CONFIGURE_COMMAND "" BUILD_COMMAND "" INSTALL_COMMAND ""
+        BUILD_BYPRODUCTS <SOURCE_DIR>/lib/libmsmpi.a)
     else()
-      # Download and configure custom MPICH files for Windows
-      message(STATUS "Downloading and configuring MPICH-1.4.1 for Windows")
-      set(MPICH2_WIN64_DEVEL_URL "${LAMMPS_THIRDPARTY_URL}/mpich2-win64-devel.tar.gz" CACHE STRING "URL for MPICH2 (win64) tarball")
-      set(MPICH2_WIN64_DEVEL_MD5 "4939fdb59d13182fd5dd65211e469f14" CACHE STRING "MD5 checksum of MPICH2 (win64) tarball")
-      mark_as_advanced(MPICH2_WIN64_DEVEL_URL)
-      mark_as_advanced(MPICH2_WIN64_DEVEL_MD5)
-
-      include(ExternalProject)
-      if(CMAKE_SYSTEM_PROCESSOR STREQUAL "x86_64")
-        ExternalProject_Add(mpi4win_build
-          URL     ${MPICH2_WIN64_DEVEL_URL}
-          URL_MD5 ${MPICH2_WIN64_DEVEL_MD5}
-          CONFIGURE_COMMAND "" BUILD_COMMAND "" INSTALL_COMMAND ""
-          BUILD_BYPRODUCTS <SOURCE_DIR>/lib/libmpi.a)
-      else()
-        ExternalProject_Add(mpi4win_build
-          URL     ${MPICH2_WIN32_DEVEL_URL}
-          URL_MD5 ${MPICH2_WIN32_DEVEL_MD5}
-          CONFIGURE_COMMAND "" BUILD_COMMAND "" INSTALL_COMMAND ""
-          BUILD_BYPRODUCTS <SOURCE_DIR>/lib/libmpi.a)
-      endif()
-
-      ExternalProject_get_property(mpi4win_build SOURCE_DIR)
-      file(MAKE_DIRECTORY "${SOURCE_DIR}/include")
-      add_library(MPI::MPI_C UNKNOWN IMPORTED)
-      set_target_properties(MPI::MPI_C PROPERTIES
-        IMPORTED_LOCATION "${SOURCE_DIR}/lib/libmpi.a"
-        INTERFACE_INCLUDE_DIRECTORIES "${SOURCE_DIR}/include"
-        INTERFACE_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
-      add_dependencies(MPI::MPI_C mpi4win_build)
-
-      # set variables for status reporting at the end of CMake run
-      set(MPI_C_INCLUDE_PATH "${SOURCE_DIR}/include")
-      set(MPI_C_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX")
-      set(MPI_C_LIBRARIES "${SOURCE_DIR}/lib/libmpi.a")
+      message(FATAL_ERROR "Only x86 64-bit builds are supported with MS-MPI")
     endif()
+
+    ExternalProject_get_property(mpi4win_build SOURCE_DIR)
+    file(MAKE_DIRECTORY "${SOURCE_DIR}/include")
+    add_library(MPI::MPI_CXX UNKNOWN IMPORTED)
+    set_target_properties(MPI::MPI_CXX PROPERTIES
+      IMPORTED_LOCATION "${SOURCE_DIR}/lib/libmsmpi.a"
+      INTERFACE_INCLUDE_DIRECTORIES "${SOURCE_DIR}/include"
+      INTERFACE_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX=1")
+    add_dependencies(MPI::MPI_CXX mpi4win_build)
+
+    # set variables for status reporting at the end of CMake run
+    set(MPI_CXX_INCLUDE_PATH "${SOURCE_DIR}/include")
+    set(MPI_CXX_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX=1")
+    set(MPI_CXX_LIBRARIES "${SOURCE_DIR}/lib/libmsmpi.a")
   else()
     find_package(MPI REQUIRED)
     option(LAMMPS_LONGLONG_TO_LONG "Workaround if your system or MPI version does not recognize 'long long' data types" OFF)
@@ -125,7 +82,7 @@ if(BUILD_MPI)
       target_compile_definitions(lammps INTERFACE -DLAMMPS_LONGLONG_TO_LONG)
     endif()
   endif()
-  target_link_libraries(lammps INTERFACE MPI::MPI_C)
+  target_link_libraries(lammps INTERFACE MPI::MPI_CXX)
 else()
   target_include_directories(lammps INTERFACE "${LAMMPS_SOURCE_DIR}/STUBS")
 endif()

From 1fc8e0564200d645a2891ea723afba8b8f6e6ef0 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Mon, 2 Jun 2025 15:48:40 -0400
Subject: [PATCH 19/23] roll back changes switching from MPI::MPI_CXX to
 MPI::MPI_C

---
 cmake/CMakeLists.txt                      | 23 +++++++++++------------
 cmake/Modules/LAMMPSInterfacePlugin.cmake |  7 ++++---
 cmake/Modules/Packages/COLVARS.cmake      |  3 +--
 cmake/Modules/Packages/GPU.cmake          |  3 +--
 cmake/Modules/Packages/ML-HDNNP.cmake     |  6 +++---
 examples/COUPLE/plugin/CMakeLists.txt     |  3 ---
 examples/COUPLE/simple/CMakeLists.txt     |  4 ++--
 examples/plugins/LAMMPSInterfaceCXX.cmake |  7 ++++---
 8 files changed, 26 insertions(+), 30 deletions(-)

diff --git a/cmake/CMakeLists.txt b/cmake/CMakeLists.txt
index b75dc92b63..cca609d8aa 100644
--- a/cmake/CMakeLists.txt
+++ b/cmake/CMakeLists.txt
@@ -203,6 +203,10 @@ if((CMAKE_SYSTEM_NAME STREQUAL "Windows") AND BUILD_SHARED_LIBS)
   set(CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS ON)
 endif()
 
+# do not include the (obsolete) MPI C++ bindings which makes for leaner object files
+# and avoids namespace conflicts. Put this early to increase its visbility.
+set(MPI_CXX_SKIP_MPICXX TRUE)
+
 ########################################################################
 # User input options                                                   #
 ########################################################################
@@ -400,28 +404,24 @@ if(PKG_ADIOS)
 endif()
 
 if(NOT CMAKE_CROSSCOMPILING)
-  find_package(MPI QUIET COMPONENTS C)
+  find_package(MPI QUIET COMPONENTS CXX)
   option(BUILD_MPI "Build MPI version" ${MPI_FOUND})
 else()
   option(BUILD_MPI "Build MPI version" OFF)
 endif()
 
 if(BUILD_MPI)
-  # do not include the (obsolete) MPI C++ bindings which makes
-  # for leaner object files and avoids namespace conflicts
-  set(MPI_CXX_SKIP_MPICXX TRUE)
   # We use a non-standard procedure to cross-compile with MPI on Windows
   if((CMAKE_SYSTEM_NAME STREQUAL "Windows") AND CMAKE_CROSSCOMPILING)
     include(MPI4WIN)
   else()
-    find_package(MPI REQUIRED COMPONENTS C)
+    find_package(MPI REQUIRED COMPONENTS CXX)
     option(LAMMPS_LONGLONG_TO_LONG "Workaround if your system or MPI version does not recognize 'long long' data types" OFF)
     if(LAMMPS_LONGLONG_TO_LONG)
       target_compile_definitions(lammps PRIVATE -DLAMMPS_LONGLONG_TO_LONG)
     endif()
   endif()
-  target_link_libraries(lammps PUBLIC MPI::MPI_C)
-  target_compile_definitions(lammps PUBLIC -DMPICH_SKIP_MPICXX -DOMPI_SKIP_MPICXX=1)
+  target_link_libraries(lammps PUBLIC MPI::MPI_CXX)
 else()
   target_sources(lammps PRIVATE ${LAMMPS_SOURCE_DIR}/STUBS/mpi.cpp)
   add_library(mpi_stubs INTERFACE)
@@ -717,7 +717,6 @@ foreach(PKG_LIB POEMS ATC AWPMD H5MD)
     file(GLOB_RECURSE ${PKG_LIB}_SOURCES CONFIGURE_DEPENDS
       ${LAMMPS_LIB_SOURCE_DIR}/${PKG_LIB}/[^.]*.c ${LAMMPS_LIB_SOURCE_DIR}/${PKG_LIB}/[^.]*.cpp)
     add_library(${PKG_LIB} STATIC ${${PKG_LIB}_SOURCES})
-    target_compile_definitions(${PKG_LIB} PUBLIC -DMPICH_SKIP_MPICXX -DOMPI_SKIP_MPICXX=1)
     set_target_properties(${PKG_LIB} PROPERTIES OUTPUT_NAME lammps_${PKG_LIB}${LAMMPS_MACHINE})
     target_link_libraries(lammps PRIVATE ${PKG_LIB})
     if(PKG_LIB STREQUAL "awpmd")
@@ -743,7 +742,7 @@ if(PKG_ATC)
     message(FATAL_ERROR "The ATC Package is not compatible with -DLAMMPS_BIGBIG")
   endif()
   if(BUILD_MPI)
-    target_link_libraries(atc PRIVATE ${LAPACK_LIBRARIES} MPI::MPI_C)
+    target_link_libraries(atc PRIVATE ${LAPACK_LIBRARIES} MPI::MPI_CXX)
   else()
     target_link_libraries(atc PRIVATE ${LAPACK_LIBRARIES} mpi_stubs)
   endif()
@@ -1057,9 +1056,9 @@ else()
 endif()
 if(BUILD_MPI)
   message(STATUS "<<< MPI flags >>>
--- MPI_defines:      ${MPI_C_COMPILE_DEFINITIONS}
--- MPI includes:     ${MPI_C_INCLUDE_PATH}
--- MPI libraries:    ${MPI_C_LIBRARIES};${MPI_Fortran_LIBRARIES}")
+-- MPI_defines:      ${MPI_CXX_COMPILE_DEFINITIONS}
+-- MPI includes:     ${MPI_CXX_INCLUDE_PATH}
+-- MPI libraries:    ${MPI_CXX_LIBRARIES};${MPI_Fortran_LIBRARIES}")
 endif()
 if(PKG_GPU)
   message(STATUS "<<< GPU package settings >>>
diff --git a/cmake/Modules/LAMMPSInterfacePlugin.cmake b/cmake/Modules/LAMMPSInterfacePlugin.cmake
index 7c71c6dae2..a449f5b3dd 100644
--- a/cmake/Modules/LAMMPSInterfacePlugin.cmake
+++ b/cmake/Modules/LAMMPSInterfacePlugin.cmake
@@ -62,6 +62,9 @@ if(CMAKE_CXX_COMPILER_ID STREQUAL "Intel")
 endif()
 set(CMAKE_POSITION_INDEPENDENT_CODE TRUE)
 
+# skip over obsolete MPI-2 C++ bindings
+set(MPI_CXX_SKIP_MPICXX TRUE)
+
 #######
 # helper functions from LAMMPSUtils.cmake
 function(validate_option name values)
@@ -128,9 +131,7 @@ endif()
 ################################################################################
 # MPI configuration
 if(NOT CMAKE_CROSSCOMPILING)
-  set(MPI_CXX_SKIP_MPICXX TRUE)
-  enable_language(C)
-  find_package(MPI QUIET COMPONENTS C)
+  find_package(MPI QUIET COMPONENTS CXX)
   option(BUILD_MPI "Build MPI version" ${MPI_FOUND})
 else()
   option(BUILD_MPI "Build MPI version" OFF)
diff --git a/cmake/Modules/Packages/COLVARS.cmake b/cmake/Modules/Packages/COLVARS.cmake
index 7b21c5804e..afef315120 100644
--- a/cmake/Modules/Packages/COLVARS.cmake
+++ b/cmake/Modules/Packages/COLVARS.cmake
@@ -27,8 +27,7 @@ if(BUILD_OMP)
 endif()
 
 if(BUILD_MPI)
-  target_compile_definitions(colvars PUBLIC -DCOLVARS_MPI -DMPICH_SKIP_MPICXX -DOMPI_SKIP_MPICXX=1)
-  target_link_libraries(colvars PUBLIC MPI::MPI_C)
+  target_link_libraries(colvars PUBLIC MPI::MPI_CXX)
 endif()
 
 if(COLVARS_DEBUG)
diff --git a/cmake/Modules/Packages/GPU.cmake b/cmake/Modules/Packages/GPU.cmake
index 4c4ace1abd..efc9f1f764 100644
--- a/cmake/Modules/Packages/GPU.cmake
+++ b/cmake/Modules/Packages/GPU.cmake
@@ -484,12 +484,11 @@ RegisterFixStyle(${GPU_SOURCES_DIR}/fix_gpu.h)
 
 get_property(GPU_SOURCES GLOBAL PROPERTY GPU_SOURCES)
 if(BUILD_MPI)
-  target_link_libraries(gpu PRIVATE MPI::MPI_C)
+  target_link_libraries(gpu PRIVATE MPI::MPI_CXX)
 else()
   target_link_libraries(gpu PRIVATE mpi_stubs)
 endif()
 
-target_compile_definitions(gpu PRIVATE -DLAMMPS_${LAMMPS_SIZES} -DMPICH_SKIP_MPICXX -DOMPI_SKIP_MPICXX=1)
 set_target_properties(gpu PROPERTIES OUTPUT_NAME lammps_gpu${LAMMPS_MACHINE})
 target_sources(lammps PRIVATE ${GPU_SOURCES})
 target_include_directories(lammps PRIVATE ${GPU_SOURCES_DIR})
diff --git a/cmake/Modules/Packages/ML-HDNNP.cmake b/cmake/Modules/Packages/ML-HDNNP.cmake
index 086432c1bf..99017f222d 100644
--- a/cmake/Modules/Packages/ML-HDNNP.cmake
+++ b/cmake/Modules/Packages/ML-HDNNP.cmake
@@ -44,7 +44,7 @@ if(DOWNLOAD_N2P2)
     set(N2P2_PROJECT_OPTIONS "-DN2P2_NO_MPI")
   else()
     # get path to MPI include directory
-    get_target_property(N2P2_MPI_INCLUDE MPI::MPI_C INTERFACE_INCLUDE_DIRECTORIES)
+    get_target_property(N2P2_MPI_INCLUDE MPI::MPI_CXX INTERFACE_INCLUDE_DIRECTORIES)
     foreach (_INCL ${N2P2_MPI_INCLUDE})
       set(N2P2_PROJECT_OPTIONS "${N2P2_PROJECT_OPTIONS} -I${_INCL}")
     endforeach()
@@ -102,9 +102,9 @@ if(DOWNLOAD_N2P2)
   # nnpif library has MPI calls if MPI is enabled, so we must link with MPI libs
   if(BUILD_MPI)
     set_target_properties(LAMMPS::N2P2::LIBNNPIF PROPERTIES
-      INTERFACE_LINK_LIBRARIES MPI::MPI_C)
+      INTERFACE_LINK_LIBRARIES MPI::MPI_CXX)
     if((CMAKE_SYSTEM_NAME STREQUAL Windows) AND CMAKE_CROSSCOMPILING)
-      add_dependencies(LAMMPS::N2P2::LIBNNPIF MPI::MPI_C)
+      add_dependencies(LAMMPS::N2P2::LIBNNPIF MPI::MPI_CXX)
     endif()
   endif()
 
diff --git a/examples/COUPLE/plugin/CMakeLists.txt b/examples/COUPLE/plugin/CMakeLists.txt
index c8deb5c7c6..4f7ab41847 100644
--- a/examples/COUPLE/plugin/CMakeLists.txt
+++ b/examples/COUPLE/plugin/CMakeLists.txt
@@ -28,9 +28,6 @@ if(MSVC)
 endif()
 
 find_package(MPI REQUIRED COMPONENTS C)
-# do not include the (obsolete) MPI C++ bindings which makes
-# for leaner object files and avoids namespace conflicts
-set(MPI_CXX_SKIP_MPICXX TRUE)
 
 ##########################
 
diff --git a/examples/COUPLE/simple/CMakeLists.txt b/examples/COUPLE/simple/CMakeLists.txt
index 6d26db1877..8396e5fb72 100644
--- a/examples/COUPLE/simple/CMakeLists.txt
+++ b/examples/COUPLE/simple/CMakeLists.txt
@@ -25,10 +25,10 @@ if(MSVC)
   add_compile_definitions(_CRT_SECURE_NO_WARNINGS)
 endif()
 
-find_package(MPI QUIET COMPONENTS C)
 # do not include the (obsolete) MPI C++ bindings which makes
 # for leaner object files and avoids namespace conflicts
 set(MPI_CXX_SKIP_MPICXX TRUE)
+find_package(MPI QUIET COMPONENTS C CXX)
 
 ##########################
 
@@ -38,7 +38,7 @@ if(NOT LAMMPS_SOURCE_DIR)
 endif()
 
 add_executable(simpleCC simple.cpp)
-target_link_libraries(simpleCC PRIVATE LAMMPS::lammps MPI::MPI_C)
+target_link_libraries(simpleCC PRIVATE LAMMPS::lammps MPI::MPI_CXX)
 
 add_executable(simpleC simple.c)
 target_link_libraries(simpleC PRIVATE LAMMPS::lammps MPI::MPI_C)
diff --git a/examples/plugins/LAMMPSInterfaceCXX.cmake b/examples/plugins/LAMMPSInterfaceCXX.cmake
index 207b579c89..6ff154dec4 100644
--- a/examples/plugins/LAMMPSInterfaceCXX.cmake
+++ b/examples/plugins/LAMMPSInterfaceCXX.cmake
@@ -33,10 +33,11 @@ endif()
 
 ################################################################################
 # MPI configuration
+# do not include the (obsolete) MPI C++ bindings which makes
+# for leaner object files and avoids namespace conflicts
+set(MPI_CXX_SKIP_MPICXX TRUE)
 if(NOT CMAKE_CROSSCOMPILING)
-  enable_language(C)
-  set(MPI_CXX_SKIP_MPICXX TRUE)
-  find_package(MPI QUIET COMPONENTS C)
+  find_package(MPI QUIET COMPONENTS CXX)
   option(BUILD_MPI "Build MPI version" ${MPI_FOUND})
 else()
   option(BUILD_MPI "Build MPI version" OFF)

From 60c33bfb957a98b3cb41bf43b667374e7a58083c Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Mon, 2 Jun 2025 16:37:21 -0400
Subject: [PATCH 20/23] correct typos

---
 cmake/Modules/MPI4WIN.cmake | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/cmake/Modules/MPI4WIN.cmake b/cmake/Modules/MPI4WIN.cmake
index b5e60616ea..cd48ab279e 100644
--- a/cmake/Modules/MPI4WIN.cmake
+++ b/cmake/Modules/MPI4WIN.cmake
@@ -18,8 +18,8 @@ endif()
 
 ExternalProject_get_property(mpi4win_build SOURCE_DIR)
 file(MAKE_DIRECTORY "${SOURCE_DIR}/include")
-add_library(MPI::MPI_C UNKNOWN IMPORTED)
-set_target_properties(MPI::MPI_CXXx PROPERTIES
+add_library(MPI::MPI_CXX UNKNOWN IMPORTED)
+set_target_properties(MPI::MPI_CXX PROPERTIES
   IMPORTED_LOCATION "${SOURCE_DIR}/lib/libmsmpi.a"
   INTERFACE_INCLUDE_DIRECTORIES "${SOURCE_DIR}/include"
   INTERFACE_COMPILE_DEFINITIONS "MPICH_SKIP_MPICXX=1")

From 07f650a98249d7c5bf08a0e4610edc31fce89872 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Mon, 2 Jun 2025 17:02:38 -0400
Subject: [PATCH 21/23] try to work around compilation issues

---
 cmake/Modules/Packages/GPU.cmake | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/cmake/Modules/Packages/GPU.cmake b/cmake/Modules/Packages/GPU.cmake
index efc9f1f764..6ce85f10c5 100644
--- a/cmake/Modules/Packages/GPU.cmake
+++ b/cmake/Modules/Packages/GPU.cmake
@@ -484,9 +484,9 @@ RegisterFixStyle(${GPU_SOURCES_DIR}/fix_gpu.h)
 
 get_property(GPU_SOURCES GLOBAL PROPERTY GPU_SOURCES)
 if(BUILD_MPI)
-  target_link_libraries(gpu PRIVATE MPI::MPI_CXX)
+  target_link_libraries(gpu PUBLIC MPI::MPI_CXX)
 else()
-  target_link_libraries(gpu PRIVATE mpi_stubs)
+  target_link_libraries(gpu PUBLIC mpi_stubs)
 endif()
 
 set_target_properties(gpu PROPERTIES OUTPUT_NAME lammps_gpu${LAMMPS_MACHINE})

From 688800038af0c8ee1b924362d22475d0369055ef Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Mon, 2 Jun 2025 20:14:11 -0400
Subject: [PATCH 22/23] force skip MPI for C++ setting into cache

---
 cmake/CMakeLists.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/cmake/CMakeLists.txt b/cmake/CMakeLists.txt
index cca609d8aa..954bd7b4ac 100644
--- a/cmake/CMakeLists.txt
+++ b/cmake/CMakeLists.txt
@@ -205,7 +205,7 @@ endif()
 
 # do not include the (obsolete) MPI C++ bindings which makes for leaner object files
 # and avoids namespace conflicts. Put this early to increase its visbility.
-set(MPI_CXX_SKIP_MPICXX TRUE)
+set(MPI_CXX_SKIP_MPICXX TRUE CACHE BOOL "Skip MPI C++ Bindings" FORCE)
 
 ########################################################################
 # User input options                                                   #

From 8a8fc2f1d8a3da601b991a60f730b677491cf905 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Mon, 2 Jun 2025 20:29:00 -0400
Subject: [PATCH 23/23] apply `-DLAMMPS_${LAMMPS_SIZES}` consistently across
 all platforms

---
 cmake/Modules/Packages/GPU.cmake | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/cmake/Modules/Packages/GPU.cmake b/cmake/Modules/Packages/GPU.cmake
index 6ce85f10c5..67d2221ec4 100644
--- a/cmake/Modules/Packages/GPU.cmake
+++ b/cmake/Modules/Packages/GPU.cmake
@@ -254,7 +254,7 @@ elseif(GPU_API STREQUAL "OPENCL")
   add_library(gpu STATIC ${GPU_LIB_SOURCES})
   target_link_libraries(gpu PRIVATE OpenCL::OpenCL)
   target_include_directories(gpu PRIVATE ${CMAKE_CURRENT_BINARY_DIR}/gpu)
-  target_compile_definitions(gpu PRIVATE -DUSE_OPENCL -D_${GPU_PREC_SETTING})
+  target_compile_definitions(gpu PRIVATE -DUSE_OPENCL -D_${GPU_PREC_SETTING} -DLAMMPS_${LAMMPS_SIZES})
   if(GPU_DEBUG)
     target_compile_definitions(gpu PRIVATE -DUCL_DEBUG -DGERYON_KERNEL_DUMP)
   else()
@@ -484,9 +484,9 @@ RegisterFixStyle(${GPU_SOURCES_DIR}/fix_gpu.h)
 
 get_property(GPU_SOURCES GLOBAL PROPERTY GPU_SOURCES)
 if(BUILD_MPI)
-  target_link_libraries(gpu PUBLIC MPI::MPI_CXX)
+  target_link_libraries(gpu PRIVATE MPI::MPI_CXX)
 else()
-  target_link_libraries(gpu PUBLIC mpi_stubs)
+  target_link_libraries(gpu PRIVATE mpi_stubs)
 endif()
 
 set_target_properties(gpu PROPERTIES OUTPUT_NAME lammps_gpu${LAMMPS_MACHINE})