Add compute style mliap to MLIAP package

[athomps]

Summary

Added a compute mliap that can be used to train model parameters for the mliap pair_style, analogous to compute snap for the snap pair styles

Related Issues

None

Author(s)

Aidan Thompson, Sandia National Laboratories

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

n/a

Implementation Notes

This compute reproduces output from the compute.snap and compute.quadratic examples in examples/snap. Those examples were also modified slightly to expose more opportunities for failure.

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
• Suitable new documentation files and/or updates to the existing docs are included
• The added/updated documentation is integrated and tested with the documentation build system
• 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
• Suitable tests have been added to the unittest tree.
• A package specific README file has been included or updated
• One or more example input decks are included

Further Information, Files, and Links

[akohlmey]

@athomps do you know why this is? should we try to do something about it? as you may recall from fixing the pair style hybrid error message, we have now better facilities to do keyword matching (and that uses only one of them).

[athomps]

Yes, my original diagnosis was wrong. The keyword snap is not silently stripped, rather it is matched to a pair style. This causes PairMLIAP::settings() to be called with a truncated argument list. Ironically, this would have worked with the old pair hybrid code, before it was fixed. I don't see a need to fix this new issue and I am okay with removing the comment "The 'p' in SNAP is dropped, because keywords that match pair_styles are silently stripped."