[gmx-users] How could I know whether I should use epsilon-sigma or c6-c12?

Bao Kai paeanball at gmail.com
Tue Jun 5 09:04:46 CEST 2012

Hi, Mark,

The values of c6-c12 parameters are different from the values of
epsilon and sigma, and they can be converted to each other.

My point is which values I should specify in my .top file.  Or it does
not matter totally and Gromacs will determine what kinds of values you
are specifying.

Thank you.


On 5/06/2012 4:34 PM, Bao Kai wrote:
> Hi, all,
> I am still trying to do my simulation with liquid mixtures.
> I have a simple question now. When I writing my .top file, how could I
> know if I should use epsilon-sigma or c6-c12 parameters for the LJ
> potential? It seems that in some examples, c6-c12 parameters are used
> and epsilon-sigma parameters are used in some other examples.

The model you are implementing chooses this and the rule by which
parameters of different atom types get combined into interaction type
parameters. The rationale for that choice often seems vague, IMO
probably doesn't matter much, and is not really your problem until you
go to design models. Literature is your friend, here.


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