[Towhee-users] rigid 12-site benzene force field

[Anatoli M. <to...@ya...>]

Hi All,

I'm trying to set up a bulk benzene simulation. I want to use completely rigid 12-site benzene model. I pulled most of the lines for a new "benzene2_ff" force field file from Charm27 ff file. Then I modified the lines, setting specific rigid bonds and angles. When I tried to skip the torsion energy parameters, setting the number of torsion types to 0, the Towhee complained, demanding to know parameters for 4-atom graphs ( CCCC, CCCH, HCCH). To make a test run, I had to resort to torsion type 8.  I was wondering if this is a good way to set up my simulation or if I might be able to skip the torsion set up at all.
The problem with setting torsion type to 8 is this. When I let Towhee (ver. 6.2.2) to initialize my molecules on the simple cubic grid, molecules are not planar. It is only when I give the explicit atomic coordinates that I get the planar molecule. 
I attach the force field file (benzene2_ff) along with the towhee input file (towhee_input).

Thank you,

Anatoli Milischuk
Department of Chemistry
Colorado State University