[gmx-users] mixing rules for LJ parameters?
Mark.Abraham at anu.edu.au
Tue Dec 19 00:49:48 CET 2006
Nicolas Winter wrote:
> I'm trying to understand how the LJ parameters are determined in the
> Gromacs FF, namely the file ffgmxnb.itp. According to the mixing rules
> given on page 88 of the manual c6 and c12 for interactions between atoms
> should just be the square root of the product of the individual atom
> parameters. However when I tried to take the individual c6 and c12 for O
> and N for example, and mix them according to this rule I come up with
> the correct number for for the O - N c6 value, but /not /for c12. So I'm
> curious how the c12 is determined? Here are the numbers I'm working
> with, the individual atom parameters taken directly from the Gromacs FF,
> file ffgmxnb.tip. The O-N values are what I get from using the mixing
> rule combination 1 on p88.
With what value are you comparing it - and what is it?
Does this arise for any other atom pairs?
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