[gmx-users] Velocity autocorrelation function

Dommert Florian dommert at icp.uni-stuttgart.de
Thu Aug 18 16:27:31 CEST 2011

On Thu, 2011-08-18 at 15:44 +0200, Elton Carvalho wrote: 
> On Mon, Aug 15, 2011 at 11:16 PM, Nilesh Dhumal <ndhumal at andrew.cmu.edu> wrote:
> > Using g_velacc I can calculate the velocity autocorrelation function of a
> > group as a vector.
> >
> > Can I calculate the velocity autocorrelation function as a scalar?

Actually I do not understand what you are pointing at. The velocity
autocorrelation function is a scalar property, as it is the dot product
of two vectors. Either I apply the -mol flag or not, two lines are
contained in vac.xvg: time vs. c(t)

However I think the description is outdated. It is claimed that for the
mol flag an index group of molecule numbers is required, but if the a
group of atoms is provided, it is split into the correct number of


> My naïve suggestion would be to take the norm of that vector.

> -- 
> Elton Carvalho
> Tel.: +55 11 3091-6985/6922
> Dept Física dos Materiais e Mecânica
> Instituto de Física
> Universidade de São Paulo
> P.O. Box 66318 - 05314-970 São Paulo-SP, Brazil

Florian Dommert
Dipl. - Phys.

Institute for Computational Physics
University Stuttgart

Pfaffenwaldring 27
70569 Stuttgart

EMail: dommert at icp.uni-stuttgart.de
Homepage: http://www.icp.uni-stuttgart.de/~icp/Florian_Dommert

Tel.: +49 - (0)711 - 68563613
Fax.: +49 - (0)711 - 68563658
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