AMBER Archive (2008)

Subject: Re: Re: AMBER: improper dihedral in ff03 united atom forcefield

From: Bill Ross (
Date: Wed Jul 23 2008 - 13:19:31 CDT

> You meant " impropers will be applied to all matching sites
> and can't be applied in the united atom forcefield".

They can be applied, but the results will likely be incorrect for
non-planar impropers.

> How can you add impropers to out-plane chiral and at the same time
> insure the consistance between torsional energy profile and quantum
> chemistry calculation ?

I have no idea what checks were made with the united atom force field
that existed at the time I was working on Leap. In general I'm not sure
how one would validate a united atom force field against quantum calcs.

> Did you think about the improper dihedral energy when deducing the
> proper dihedral parameters?

I didn't do any of the force field work. My task was to make Leap
replicate the results from the previous programs (Link, Edit, and Parm).

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