Re: AMBER: Using OPLS atom types

From: Bill Ross <>
Date: Sat, 3 Dec 2005 10:15:53 -0800 (PST)

> > I am trying to use OPLS atom type in amber, i have altered the
> > opls_parm.dat file to the new format and removed the non-bonded STDU
> > and STUB vdw parameters and everything seems OK, except that the "AC"
> > flag which specifies c6-c12 style params instead of "RE" for radius,
> > thus the vdw energy is ridiculous.
> >
> > Is there another flag to specify the format of the vdw parameters
> > which must be set in leap?
> As far as I can tell/remember, LEaP doesn't have an option to read in the AC
> parameters from this file. It doesn't look like it would be hard to make this
> modification, but I don't think it has ever been done.
> Maybe someone with a better memory or familiarity with the code will be able
> to correct me on this.... (Bill?)

The main obstacle to implementing united-atom ff's in leap is
to come up w/ a way to handle nonplanar improper torsions.
Without this in hand, there isn't much point to adding AC
handling. Also note that ff's that use AC instead of R*,e
may be more likely to use different combining rules, and
thus need conversion as was done with Aqvist parameters. (I
don't know if this was done with OPLS, or whether the old
parm code handled it.)

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Received on Sat Dec 03 2005 - 18:53:00 PST
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