[gmx-users] OPLS question

[Jee E Rim]

Hi,

I'm trying to put together a topology for a nicotine analogue molecule using the OPLS forcefield.

Most of the atom types that I need and the force field parameters are already in the OPLS force field, except for a couple of dihedrals. So, I ran a series of single point calculations using Gaussian98 to get the energies of the configuration with the dihedral angles changing from 0 to 360, and am attempting to get the dihedral coefficients by a least-squares fitting to the Ryckaert-Bellemans potential function. Is this a good way to get the dihedral parameters? I'm using the optimized geometry I get from Gaussian, and am just changing the dihedral angles.

The second question is, in the manual it's stated that, with the RB potential, the 1-4 interactions must be excluded, is this also the case when you're using the OPLS force field? And should I also exclude the 1-4 interactions when I'm using the parameters derived as above? 

Thanks for your help in advance!
Jee.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://maillist.sys.kth.se/pipermail/gromacs.org_gmx-users/attachments/20040525/2d4a7321/attachment.html>