EspalomaCharge toolkit wrapper generates np.float32 charges, but np.float64 are expected

[jchodera]

I'm tracking down an odd issue where it seems like the pint.Quantity wrapped np.float32 is causing problems when molecule.to_openeye() is called afterwards:

Traceback (most recent call last):
  File "/lila/data/chodera/chodera/espaloma_charge/scripts/hydration-free-energies/compare-models.py", line 265, in <module>
    cli()
  File "/lila/home/chodera/miniconda/envs/hydration/lib/python3.10/site-packages/click/core.py", line 1130, in __call__
    return self.main(*args, **kwargs)
  File "/lila/home/chodera/miniconda/envs/hydration/lib/python3.10/site-packages/click/core.py", line 1055, in main
    rv = self.invoke(ctx)
  File "/lila/home/chodera/miniconda/envs/hydration/lib/python3.10/site-packages/click/core.py", line 1657, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/lila/home/chodera/miniconda/envs/hydration/lib/python3.10/site-packages/click/core.py", line 1404, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/lila/home/chodera/miniconda/envs/hydration/lib/python3.10/site-packages/click/core.py", line 760, in invoke
    return __callback(*args, **kwargs)
  File "/lila/data/chodera/chodera/espaloma_charge/scripts/hydration-free-energies/compare-models.py", line 194, in errors
    oemol = charged_molecule.to_openeye()
  File "/lila/home/chodera/miniconda/envs/hydration/lib/python3.10/site-packages/openff/toolkit/topology/molecule.py", line 4791, in to_openeye
    return toolkit_registry.call(
  File "/lila/home/chodera/miniconda/envs/hydration/lib/python3.10/site-packages/openff/toolkit/utils/toolkit_registry.py", line 356, in call
    raise e
  File "/lila/home/chodera/miniconda/envs/hydration/lib/python3.10/site-packages/openff/toolkit/utils/toolkit_registry.py", line 352, in call
    return method(*args, **kwargs)
  File "/lila/home/chodera/miniconda/envs/hydration/lib/python3.10/site-packages/openff/toolkit/utils/openeye_wrapper.py", line 1504, in to_openeye
    oe_atom.SetPartialCharge(
  File "/lila/home/chodera/miniconda/envs/hydration/lib/python3.10/site-packages/openeye/oechem.py", line 13912, in SetPartialCharge
    return _oechem.OEAtomBase_SetPartialCharge(self, arg2)
TypeError: in method 'OEAtomBase_SetPartialCharge', argument 2 of type 'double'

but np.float64 generated by the other toolkit wrappers appears to be fine.

I'll try to create a minimal test case here once I figure out what is going on.

In the meantime, I'll make changes to follow this convention used in the toolkit in the hydration branch.

[mikemhenry]

@jchodera did you ever track this down? or an easy reproducer we can add to our CI?