What exactly do you mean with 'the function is only fit to a single
fourier term' ? The E_tors can have as many cosine terms in it as
possible. For instance, in the parm99.dat file, you have the following
torsion defined:
CT-CT-CT-CT 1 0.18 0.0 -3.
CT-CT-CT-CT 1 0.25 180.0 -2.
CT-CT-CT-CT 1 0.20 180.0 1.
This parameter set is to define the torsion energy of CT-CT-CT-CT with
different PHASE, PK, and PN values (IDIVF is equal to 1) which will have 3
cosine term to define the CT-CT-CT-CT torsional energy. You can increase
the level of accuracy by increasing the number of cosine terms used to
define a particular torsion.
Ilyas Yildirim, Ph.D.
---------------------------------------------------------------
= Hutchison Hall B#10 - Department of Chemistry =
= - University of Rochester =
= 585-275-6766 (office) - =
=
http://www.pas.rochester.edu/~yildirim/ =
---------------------------------------------------------------
On Mon, 15 Feb 2010, stephane acoca wrote:
> Hi, I would like to clarify the protocol for adjusting torsional
> parameters. The problem I am having is that after fitting to a fourier
> series the energy difference between the QM and MM energies (torsion
> not included in MM Energy), the frcmod specifications I find point to
> :
>
> IDIVF
> PK
> PHASE
> PN
>
> Meaning that the function is only fit to a single fourier term of the format :
>
> Etors = (PK/IDIVF)*(1+ COS(PN*PHI - PHASE)
>
> Aren't higher level fourier terms available to be specified torsion
> parameters. I couldn't find the information in either Amber manual
> 8,9, or 10. Any guidance would be appreciated.
>
> Stephane Acoca
> McGill University
>
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>
>
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Received on Mon Feb 15 2010 - 08:30:03 PST
