SMIRNOFF: Can handlers of the same type with different functional forms co-exist?

[mattwthompson]

I don't know the best language to use here, but I think I can get the message across with an example. Assume some future version of the SMIRNOFF spec allows for morse bond potentials, and a force field would like to use harmonic potentials for most bonds but morse potentials for other bonds. (Torsions are probably a more realistic example.) How should this be encoded, and should there be any restrictions? If split out, like

<Bonds version="2.0" potential="harmonic">
    ...
</Bonds>
<Bonds version="2.0" potential="morse">
    ...
</Bonds>

how would parameter precedence be resolved?

This is potentially a headache for implementation, and that's probably where most of the the responsibility lies.

[davidlmobley]

My first reaction is that this seems so painful/dangerous/confusing that we might want to insist all instances of a parameter type have the same functional form. But... maybe there are cases where we really really want different forms...?

[SimonBoothroyd]

But... maybe there are cases where we really really want different forms...?

My +1 would be to start restrictive (i.e. forbid mixing of FF forms), and loosen the restrictions when / if someone does eventually want this supported, with the caveat that the lobbying person should have a clear use case for enabling this. Otherwise you're building in complexity that will probably never be touched.