Re: NBFix command to apply Lorentz-Berthelot mixing rules

From: Jim Phillips (
Date: Mon Aug 22 2005 - 18:33:41 CDT

Lorentz-Berthelot mixing rules (geometric epsilon, arithmetic sigma) are
the default for NAMD (and the CHARMM force field). You have to explicitly
enable geometric sigma combining for OPLS.

If that doesn't do what you want, NBFix goes in the parameter file but I
don't know that they've ever been tested since you never see them anymore.


On Sun, 21 Aug 2005, Joshua D. Moore wrote:

> Hi,
> I have recently discovered in the NAMD 1.5 manual a description of the
> 'NBFix' command where the Lenard Jones mixed parameters can be applied
> explicitly. I am using OPLS, which uses the geometric combining rule for
> both sigma and epsilon. However, I thought that between unlike atoms I
> might want to apply the Lorentz-Berthelot mixing rules.
> Can the 'NBFix' command still be used in NAMD to explicitly state the
> sigma,ij, and epsilon,ij (and modified 1-4 interactions as well)? If so,
> does anyone have an example input for this? Does it go in the
> configuration file or in the parameter file?
> Thanks.
> Joshua Moore

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