New example/UNITS dir

[sjplimp]

Summary

Provide 3 input scripts that simluate the same physical system (LJ liquid argond) in 3 different LAMMPS units: lj, real, metal. They illustrate how to scale/unscale input/output quantities between unit systems, so that users can hopefully do this for any input script they might need to.

Related Issues

Questions about how to do this arise occasionally on the mail list.

Author(s)

Steve

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

Provide any relevant details about how the changes are implemented, how correctness was verified, how other features - if any - in LAMMPS are affected

Post Submission Checklist

Please check the fields below as they are completed after the pull request has been submitted. Delete lines that don't apply

• 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
• A package specific README file has been included or updated
• One or more example input decks are included

Further Information, Files, and Links

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[akohlmey]

@ellio167 @tadmor perhaps this folder is a good place to contribute some example cases for the KIM package unit conversion features. There is an Argon model in your data base, so you could start from the examples here.