Support modified scee/scnb in OpenMM export #1136
Description
It would be useful if we could add the ability to export OpenMM systems with modified scee and scnb nonbonded scaling parameters. Attempting to convert the AMBER GLYCAM06j-1 glycan force field yields the following error:
Traceback (most recent call last):
File "convert_amber.py", line 1277, in <module>
main()
File "convert_amber.py", line 107, in main
convert_yaml(args.input, ffxml_dir='ffxml/')
File "convert_amber.py", line 420, in convert_yaml
ffxml_name = convert_leaprc(files, ffxml_dir=ffxml_dir, ignore=ignore,
File "convert_amber.py", line 212, in convert_leaprc
params.write(ffxml_name, provenance=provenance, write_unused=write_unused, improper_dihedrals_ordering='amber')
File "/Users/choderaj/miniconda/envs/openmmforcefields/lib/python3.8/site-packages/parmed/openmm/parameters.py", line 65, in wrapper
return func(*args, **kwargs)
File "/Users/choderaj/miniconda/envs/openmmforcefields/lib/python3.8/site-packages/parmed/openmm/parameters.py", line 368, in write
self._write_omm_nonbonded(root, skip_types, separate_ljforce)
File "/Users/choderaj/miniconda/envs/openmmforcefields/lib/python3.8/site-packages/parmed/openmm/parameters.py", line 65, in wrapper
return func(*args, **kwargs)
File "/Users/choderaj/miniconda/envs/openmmforcefields/lib/python3.8/site-packages/parmed/openmm/parameters.py", line 886, in _write_omm_nonbonded
raise NotImplementedError('Cannot currently handle mixed 1-4 '
NotImplementedError: Cannot currently handle mixed 1-4 scaling: Elec. Scaling factors 1.0, 1.2 detected