Re: [AMBER] Modified force fields

From: David A Case <>
Date: Tue, 10 Mar 2020 14:38:36 -0400

On Tue, Mar 10, 2020, ankita mehta wrote:
>3. I am getting some warning when I load modified FF as follows:
>Improper torsion lines
>I want to correct this warning...

This is a tough issue. There are expected "missing" improper torsions
for systems with fused rings (like purines and tryptophan). This arose
about 35 years ago when someone (and it wasnt' me...) decided that a few
milliseconds (back then, a few microseonds now) could be saved by by
leaving these out of the force field, rather than having them in there
with zero force constants.

The obvious problem is that real warnings about missing impropers can
get lost in the midst of these innocuous ones. I'm hoping that *some*
Amber user would like to get a gold star by adding in the zero-force
constant impropers that are needed to remove the warnings for standard
proteins and nucleic acids....

Most likely, however: you can just ignore these warnings for now.
That's what everyone else does....


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Received on Tue Mar 10 2020 - 12:00:02 PDT
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