Added minimal info on downloading and building PACE library

doc/src/Build_extras.rst

@@ -52,6 +52,7 @@ This is the list of packages that may require additional steps.
    * :ref:`USER-MESONT <user-mesont>`
    * :ref:`USER-MOLFILE <user-molfile>`
    * :ref:`USER-NETCDF <user-netcdf>`
+   * :ref:`USER-PACE <user-pace>`
    * :ref:`USER-PLUMED <user-plumed>`
    * :ref:`USER-OMP <user-omp>`
    * :ref:`USER-QMMM <user-qmmm>`
@@ -1247,6 +1248,37 @@ be built for the most part with all major versions of the C++ language.
 
 ----------
 
+.. _user-pace:
+
+USER-PACE package
+-----------------------------
+
+This package requires a library that can be downloaded and built 
+in lib/pace or somewhere else, which must be done before building 
+LAMMPS with this package. 
+
+.. tabs::
+
+   .. tab:: CMake build
+
+      The library download and build will happen automatically when USER-PACE
+      is requested.
+
+   .. tab:: Traditional make
+
+      You can download and build the USER-PACE library
+      in one step from the ``lammps/src`` dir, using these commands, 
+      which invoke the ``lib/pace/Install.py`` script. 
+
+      .. code-block:: bash
+
+         $ make lib-pace                          # print help message
+         $ make lib-pace args="-b"                # download and build the default version in lib/pace
+
+      You should not need to edit the ``lib/pace/Makefile.lammps`` file.
+
+----------
+
 .. _user-plumed:
 
 USER-PLUMED package

doc/src/Packages_details.rst

@@ -1378,6 +1378,10 @@ Aidan Thompson^3, Gabor Csanyi^2, Christoph Ortner^4, Ralf Drautz^1.
 
  ^4: University of British Columbia, Vancouver, BC, Canada
 
+**Install:**
+
+This package has :ref:`specific installation instructions <user-pace>` on the :doc:`Build extras <Build_extras>` page.
+
 **Supporting info:**
 
 * src/USER-PACE: filenames -> commands

src/USER-PACE/README

@@ -1,18 +1,18 @@
-The USER-PACE package,
+The USER-PACE package provides the pace pair style, 
-provides the pace pair style, an efficient implementation of 
+an efficient implementation of the Atomic Cluster Expansion 
-the Atomic Cluster Expansion potential (ACE).
+potential (ACE).
-ACE is a methodology for deriving a highly accurate classical potential
+
-fit to a large archive of quantum mechanical (DFT) data. 
+ACE is a methodology for deriving a highly accurate classical 
+potential fit to a large archive of quantum mechanical (DFT) data. 
 This package was written by Yury Lysogorskiy and others
 at ICAMS, the Interdisciplinary Centre for Advanced Materials Simulation, 
-Ruhr University Bochum, Germany, http://www.icams.de
+Ruhr University Bochum, Germany (http://www.icams.de).
 
 This package requires a library that can be downloaded and built 
-in lib/pace or somewhere else, 
+in lib/pace or somewhere else, which must be done before building 
-which must be done before building LAMMPS with this
+LAMMPS with this package. Details of the download, build, and 
-package. Details of the download, build, and install process for
+install process for this package using traditional make (not CMake) 
-this package usng traditional make (not CMake) are given in the 
+are given in the lib/pace/README file, and scripts are
-lib/pace/README file, and scripts are
 provided to help automate the process.  Also see the LAMMPS manual for
 general information on building LAMMPS with external libraries
 using either traditional make or CMake.