Print warning when writing PairCoeff section in data file may not sufficiently reproduce all pair coefficients

[akohlmey]

Summary

The write_data command will be default always write out a PairCoeff section which includes only the pair_coeff parameters for itype == jtype. This PR adds code to detect if a pair_coeff command was explicitly run for itype != jtype and then print a warning when writing a data file, that the option pair ij is needed, i.e. requesting to write a PairIJCoeff section, to fully reproduce the pairwise force field settings.

Author(s)

Axel Kohlmeyer, Temple U

Licensing

By submitting this pull request, I agree, that my contribution will be included in LAMMPS and redistributed under either the GNU General Public License version 2 (GPL v2) or the GNU Lesser General Public License version 2.1 (LGPL v2.1).

Backward Compatibility

Yes.

Implementation Notes

I have been thinking about having this flag determine the default for the pair keyword for write_data, but that would change behavior and printing a warning should be sufficient to alert people (and definitely preferable to silently writing out different force field data).

Post Submission Checklist

• The feature or features in this pull request is complete
• Licensing information is complete
• Corresponding author information is complete
• The source code follows the LAMMPS formatting guidelines
• The feature has been verified to work with the conventional build system
• The feature has been verified to work with the CMake based build system