[gmx-users] CHARMM ff cutoffs

[João Henriques]

Dear all,

Is there any piece of literature that explicitly states what is the *de
facto* cutoff for CHARMM FFs, i.e., for the LJ and electrostatic
interactions? The old gromacs site states it's 1.2 nm:

http://www.gromacs.org/Documentation/Terminology/Force_Fields/CHARMM

However, I've read Robert Best's C36 and Huang's C36m papers, along with
older CHARMM ff publications by MacKerell and Co., and I'm rather confused
at this point. E.g., on the C36m paper, the RS peptide is simulated with
0.95 nm cutoffs and other proteins with 1.2 nm. Robert is consistent and
uses 1.2 nm all the way. Older publications use even shorter cutoffs.

I know the cutoffs can probably be toyed with to a certain extent (Stefano
Piana and Kresten Lindorff-Larsen showed that on their 2012 paper), but a
recent paper by Davide Mercadante on JCTC seems to show that it is not so
simple for IDPs, and shortening the cutoffs is a no-no (even though he did
it for his KBFF and AMBER FFs, not CHARMM).

In my work I use CHARMM36m with 1.2 nm, but, looking at the literature,
there's no way I can justify my choice when the original C36m does not
stick to a single cutoff selection...

I know Justin is/was affiliated with the MacKerell lab, so maybe he can
shed some light on this subject. Anyone else is encouraged to give their
input as well.

Thank you in advance,
Best regards,
João