[gmx-users] modify C6 directly in FF using sigma and epsilon

[Ryogo Sugitani]

David,

How about adding [ nonbond_params ] in your ff???nb.itp file
as shown in p.88 of the user's manual?
I believe it will override the default vdw interaction for that
particular atom-type pair.
(Assuming you want to use combination rule #1 just for that atom-type pair)

If I miss your point, please disregard this...


Ryogo


2007/4/5, David Mobley <dmobley at gmail.com>:
> Gromacs users,
>
> I'm using a force field (the port of AMBER to GROMACS) which uses
> combination rules (combination rule 2), etc. in terms of sigma and
> epsilon. However, I need to be able to modify C6 directly (in
> particular, I want to be able to set it to zero). Can anyone give me
> any pointers on a relatively straightforward way to do that? I want to
> be able to continue using combination rule 2 but be able to separately
> modify C6 for a couple atom types (or interacting atom pairs).
>
> Obviously, one way I could work around this would be to explicitly
> specify all of the nonbonded interaction pairs in my topology so that
> the combination rules aren't used, then I could change the combination
> rule so that I could modify C6 and C12. But since that would be a real
> pain I'm hoping someone here can suggest something easier.
>
> Thanks,
> David
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