espaloma.graphs.utils.offmol_indices.improper_torsion_indices

espaloma.graphs.utils.offmol_indices.improper_torsion_indices(offmol: openff.toolkit.topology.molecule.Molecule, improper_def='espaloma') → numpy.ndarray

“[:1]~[X3:2](~[:3])~[:4]” matches (_all_improper_torsion_indices returns “[:1]~[:2](~[:3])~[*:4]” matches)

improper_def allows for choosing which atom will be the central atom in the permutations: smirnoff: central atom is listed first espaloma: central atom is listed second

Addtionally, for smirnoff, only take the subset of atoms that corresponds to the ccw traversal of connected atoms.

Notes

Motivation: offmol.impropers returns a large number of impropers, and we may wish to restrict this number. May update this filter definition based on discussion in https://github.com/openff.toolkit/openff.toolkit/issues/746