# [gmx-developers] modify forces

Nguyen Hoang Phuong phuong at theochem.uni-frankfurt.de
Mon Apr 5 12:27:57 CEST 2004

Dear Developers,

let consider a dihedral angle formed by 4 atoms: i,j,k,l. The
dihedral potential energy is V(\theta_{ijkl}). I would like to modify the
force acting on the atoms i,j,k,l as the following

f'_i = (V/KT)*f_i
f'_j = (V/KT)*f_j
f'_k = (V/KT)*f_k
f'_l = (V/KT)*f_l

where f_i is the standard force (= dV/dr_i).

I had a look at the subroutine do_dih_fup.c of the bondfree.c but I could
not find the expressions of the forces where I can change. Can anyone
help me? Thank you very much in advance.

Phuong