AMBER Archive (2009)

Subject: [AMBER] dihedral force calculation

From: Germain Vallverdu (germain.vallverdu_at_lcp.u-psud.fr)
Date: Fri Sep 11 2009 - 09:35:08 CDT

Dear amber users

I am trying to understand the cartesian forces calculations in the case
of a dihedral potential. The source code of this calculation is in
dihedrals.f90 module.

I supposed that the following is used

f = - d E(phi) / d r = 1/sin phi * dE(phi)/d phi * d cos phi / d r

and then with special stuff if sin phi tends to zero we, get the
following equation :

f = - df * d cos phi / d r (line 344 in dihedrals.f90 in pmemd in
amber 10)

I do not understand the calculation of the cos phi derivative. But maybe
I can let it for later. I think this calculation
is the one describe in Allen and Tildesley.

I juste would like to know if my previous equation is right. Mainly is
the minus sign correct ?

Thanks for your help.

germain 

-- 
Germain Vallverdu
Doctorant
Laboratoire de Chimie Physique
germain.vallverdu_at_lcp.u-psud.fr
01 69 15 30 38

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