SMIRNOFF: "No cutoff" vdW interactions not allowed

[mattwthompson]

It would be useful for testing purposes (and possibly some gas-phase small molecule studies, I'm not sure) to allow for vdW interactions to not be truncated at all. This is dubious for most applications that people care about, since an "all-all" neighbor list is not tractable for anything but small configurations.

I don't know what other engines this is implemented in; I don't think GROMACS supports it. OpenMM implements openmm.NonbondedForce.NoCutoff.

[davidlmobley]

In GROMACS you would presumably just need to make the cutoff larger than the size of the molecule, so it's indirectly supported. And I agree with you that this would be useful.

[mrshirts]

In GROMACS you would presumably just need to make the cutoff larger than the size of the molecule, so it's indirectly supported. And I agree with you that this would be useful.

Yes, though you should also turn off periodic boundary conditions, or make them quite large just to be sure.

[mattwthompson]

With OFF-EP 0008 #53 there is now a "no-cutoff" option that does what I believe it intended here in version 0.4 of the vdW section.

Note that the toolkit doesn't support it yet, but there should be an upcoming change to vdWHandler that does.