AMBER Archive (2008)

Subject: AMBER: dihedral potential with odd periodicity

From: Germain Vallverdu (
Date: Tue Jun 24 2008 - 09:43:26 CDT


I am trying to do a force field for a non standard residue. I computed new charges, create new atoms type ect ... Now I would like to fit dihedral potential on my QM calculations. Then I tried to fit with a sum of AMBER dihedral potentiel function like :

Etors = Vn / N * [1 + cos( n * phi - gamma ) ]

My problem comes with n. If I choose n=1 or 3, when phi moves from 0 to 180° Etors remains equal at Vn . If I choose n=2 or 4 it works correctly. I tried to change hybridation of carbon but this do nothing. I tried also with CT type for carbon and this do nothing.

I did tests on ethene and I join the results on the zip file. There is frcmod topology tleap procedure and results.

I use AMBER 9.



Germain Vallverdu
Laboratoire de Chimie Physique
Université Paris Sud 11
01 69 15 30 38 / 06 88 59 08 87
Chacun de nous a son étoile. Suivons la en nous félicitant de la voir chaque jour un peu plus loin ! (V. Grignard)

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