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## Re: [ESPResSo-users] Questions regarding gaussian potential

**From**: |
Axel Arnold |

**Subject**: |
Re: [ESPResSo-users] Questions regarding gaussian potential |

**Date**: |
Wed, 05 Jun 2013 00:00:16 +0200 |

**User-agent**: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130510 Thunderbird/17.0.6 |

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
--
JP Dr. Axel Arnold Tel: +49 711 685 67609
ICP, Universität Stuttgart Email: address@hidden
Allmandring 3
70569 Stuttgart, Germany