AlchemicalFunctions for subgroups of atoms

[chabi-fin]

Hello!

I was confused on how to use AlchemicalFunction to apply different lambda values to different subgroups of atoms.
In my set up, I would like to annihilate a charged molecule with neutral co-alchemical ions.
This looks like:

1. switching off the electrostatics for the molecule + co-alchemical ions
2. switching off the sterics for the molecule, leaving the co-alchemical ion sterics unperturbed

Some advice has been provided on using a step function approach, but how to additionally tune atom grouping?

Thanks!
-Lauren