[gmx-users] Using Morse potentials with ENCAD force field

[Andy Shelley]

Actually I think I am using the gromos force field. I have been using
Christopher Stiles page as a guide to get started with using CNT
http://cs86.com/CNSE/SWNT.htm. I realize now that all the modifications were
made to ffgmx files.  So I believe I am using the gromos forcefield. Is the
forcefield used defined by the parameters? I have added nonbonded parameters
to ffgmxnb.itp as the following:
[ nonboned_params ]
   O    N    1 0.0069        1.4016E-05
    O    O    1 0.0061        9.9676E-06
    N    N    1 0.0076        1.8778E-05
    C    O    1 0.0030        4.7908E-06
    C    N    1 0.0033        6.5271E-06

and the same for pairtypes
 [ pairtypes ]
    C    N    1  0.0033       6.5271E-06
    C    O    1  0.0030       4.7908E-06
    N    N    1  0.0076       1.8778E-05
    O    O    1  0.0061       9.9676E-06
    O    N    1  0.0069       1.4016E-05

I have put just 200 nitrogen molecules in a 24.7nm x 24.7nm x 12.3nm box
with a 10,10 cnt length 12.3nm.  The nitrogen molecules appear to not even
interact with the cnt but it still flattens.  Any ideas?

Thanks,
Andy
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