Re: [ESPResSo-users] Questions regarding gaussian potential

[Axel Arnold]

On 06/03/2013 06:00 PM, Salvador H-V wrote:
> Dear All,
>
> I have a  a monodisperse system in 3D interacting via the gaussian 
> core model (GCM) potential. I have been trying to reproduce some 
> reported results without success.
>
> I had noted that the ESPResSo implementation of the GCM uses an 
> "extra" factor of 0.5. Because I have not found such definition in 
> published papers... I was wondering where this factor comes from?

It is simply a standard Gaussian exp[-x^2/(2 sigma^2)]. Mathematically, 
the 2 comes in so that sigma^2 is really the variance of the Gaussian. 
In any case, you can obviously just scale the incoming sigma by 
1/sqrt(2) to get the form without 1/2.

> More important, if I want to simulate the GCM without such 1/2 factor, 
> all that I have to do is just to modify the file "gaussian.h" in the 
> src folder, right?  Or are there more files that should be modified?

No, see above, just adjust the variance. There is no point in taking out 
the 1/2, and you would need to be careful to get the forces scale correctly.

> My last question is regarding how espresso calls the gaussian.h file. 
> If I remove such file ESPREsSo should complain because it does not 
> exist the file, right? I am asking because I already did some 
> modifications in the gaussian.h file and forces and energies are the 
> same that using the original file. Besides I renamed the gaussian.h 
> file (there is not gaussian.h file anymore)  and ESPResSo still 
> continues running without any complaining.
Did you recompile? The headers are not called, but used to create the 
binary. Since deleting gaussian.h makes it impossible to compile, the 
binary will remain untouched and the old one. Therefore, even if 
compiling actually doesnt work anymore, Espresso of course still runs, 
just unchanged. Just check the modification time of the binary.

Axel


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JP Dr. Axel Arnold           Tel: +49 711 685 67609
ICP, Universität Stuttgart   Email: address@hidden
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