evaluator unit bug

[wenyan4work]

there is a unit bug when forcebalance is used with openff-evaluator: openforcefield/openff-evaluator#482

The bug happens at the unit parsing and conversion part in evaluator_io.py:

forcebalance/src/evaluator_io.py

Line 353 in da8346c

if not isinstance(parameter_value, simtk_unit.Quantity):

If we print the type and value before and after that line:

        print('parameter_value 0: ', parameter_value)
        print('type: ', type(parameter_value))
        if not isinstance(parameter_value, simtk_unit.Quantity):
            parameter_value = parameter_value * simtk_unit.dimensionless
            print('parameter_value 1: ', parameter_value)
            print('type: ', type(parameter_value))

we get

parameter_value 0:  5.27e-05 kilocalorie / mole
type:  <class 'pint.util.Quantity'>
parameter_value 1:  5.27e-05 dimensionless kilocalorie / mole
type:  <class 'pint.util.Quantity'>

after openff-units package was introduced, parameter_value is already a pint Quantity, but since it is not a simtk_unit.Quantity, it is multiplied by a dimensionelss number, then in the following step

forcebalance/src/evaluator_io.py

Line 356 in da8346c

return openmm_quantity_to_pint(parameter_value), is_cosmetic

it is converted to a dimensionless quantity.

How to fix this?
Perhaps the easiest change is to modify the last line of L356 to return parameter_value, is_cosmetic, I got the following error: