[gmx-users] torsion potential with 7 parameters

[David van der Spoel]

Ángel Piñeiro wrote:
> Hi all,
> anyone knows how to use (in gromacs) a potential of the type:
> 
> U_tors(phi_ijkl) = Sum_n 1/2 k_n [1-cos(n phi_ijkl)]
> 
> with n going from 1 to 7?
> 
> as far as I saw only the Ryckaert-Bellemans with 6 parameters and a
> periodic function are implemented in gromacs. Chapter 4 says something
> about this subject and it explains how to translate OPLS in R-B but it
> seems that 7 parameters are not included
> 
> I am trying to use the force field for perfluoroalkanes published by
> Borodin et al in JPCB (106) 2002, 9912.


in the worst case you can add two dihedrals, however n = 6,7 is not 
implemented. you can however tabulate this if I'm not mistaken.

> Thanks in advance for the help,
> 
> Angel Piñeiro.
> 
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-- 
David van der Spoel, Ph.D.
Molec. Biophys. group, Dept. of Cell & Molec. Biol., Uppsala University.
Box 596, 75124 Uppsala, Sweden. Phone:	+46184714205. Fax: +4618511755.
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://folding.bmc.uu.se