From a7f4bbffcfc60fdf25a25e2c9f6c039622aa58dd Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Thu, 26 Aug 2021 07:10:47 -0400
Subject: [PATCH] avoid segfault when trying to apply (strict) pbc or convert
 to/from fractional coordinates on an MPI rank without atoms

---
 src/OPENMP/domain_omp.cpp | 10 +++++++---
 src/domain.cpp            |  3 ++-
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/src/OPENMP/domain_omp.cpp b/src/OPENMP/domain_omp.cpp
index 94a0b094a7..dffb58e2da 100644
--- a/src/OPENMP/domain_omp.cpp
+++ b/src/OPENMP/domain_omp.cpp
@@ -37,6 +37,9 @@ typedef struct { double x,y,z; } dbl3_t;
 
 void DomainOMP::pbc()
 {
+  const int nlocal = atom->nlocal;
+  if (!nlocal) return;
+
   dbl3_t * _noalias const x = (dbl3_t *)&atom->x[0][0];
   dbl3_t * _noalias const v = (dbl3_t *)&atom->v[0][0];
   const double * _noalias const lo     = (triclinic == 0) ? boxlo : boxlo_lamda;
@@ -44,7 +47,6 @@ void DomainOMP::pbc()
   const double * _noalias const period = (triclinic == 0) ? prd   : prd_lamda;
   const int * _noalias const mask  = atom->mask;
   imageint    * _noalias const image = atom->image;
-  const int nlocal = atom->nlocal;
 
 #if defined(_OPENMP)
 #pragma omp parallel for LMP_DEFAULT_NONE schedule(static)
@@ -141,8 +143,9 @@ void DomainOMP::pbc()
 
 void DomainOMP::lamda2x(int n)
 {
-  dbl3_t * _noalias const x = (dbl3_t *)&atom->x[0][0];
   const int num = n;
+  if (!n) return;
+  dbl3_t * _noalias const x = (dbl3_t *)&atom->x[0][0];
 
 #if defined(_OPENMP)
 #pragma omp parallel for LMP_DEFAULT_NONE schedule(static)
@@ -161,8 +164,9 @@ void DomainOMP::lamda2x(int n)
 
 void DomainOMP::x2lamda(int n)
 {
-  dbl3_t * _noalias const x = (dbl3_t *)&atom->x[0][0];
   const int num = n;
+  if (!n) return;
+  dbl3_t * _noalias const x = (dbl3_t *)&atom->x[0][0];
 
 #if defined(_OPENMP)
 #pragma omp parallel for LMP_DEFAULT_NONE schedule(static)
diff --git a/src/domain.cpp b/src/domain.cpp
index 7df82fbfb3..958c3f09db 100644
--- a/src/domain.cpp
+++ b/src/domain.cpp
@@ -528,10 +528,11 @@ void Domain::reset_box()
 
 void Domain::pbc()
 {
+  int nlocal = atom->nlocal;
+  if (!nlocal) return;
   int i;
   imageint idim,otherdims;
   double *lo,*hi,*period;
-  int nlocal = atom->nlocal;
   double **x = atom->x;
   double **v = atom->v;
   int *mask = atom->mask;