Hi,

 if you want to calculate the MSD of several molecules, say nrmol, without 
using the
-mol option, which I do not know is still broken, you can do this in
three simple steps:

1. Convert your trajectory with trjconv and the option -pbc whole
2. Create an index file, that contains groups, which contain one
   molecule each, and remove the standard groups like System ...
3. run the analysis with: echo {0..nrmol} | g_msd -f convertedtrajecotry
-n indexfile -ng nrmol

This gives you the correct MSD for the center of mass for every
molecule.

Cheers,
Flo


* George Patargias <g...@bioacademy.gr> [2013-05-02 10:08:20 +0300]:

Thanks for this Vitaly and Justin.
George

The resulting MSD will correspond to the average from individual atoms.

Calculating MSD of an individual atom and ascribing it to a [small]
molecule, which this atom belongs to, is reasonable. Assuming that
averaged
MSD from atoms correspond to the cluster they form is not.


Dr. Vitaly Chaban




On Wed, May 1, 2013 at 2:40 PM, George Patargias <g...@bioacademy.gr>
wrote:

Hello

I am trying to calculate the MSD of 8 molecules in a lipid bilayer with
g_msd. If I include the atoms of all these 8 molecules as a single group
in the index file, will g_msd calculate the MSD of the center of mass of
them or it will average over all atoms?


Thanks
George


Dr. George Patargias
Postdoctoral Researcher
Biomedical Research Foundation
Academy of Athens
4, Soranou Ephessiou
115 27
Athens
Greece

Office: +302106597568






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Dr. George Patargias
Postdoctoral Researcher
Biomedical Research Foundation
Academy of Athens
4, Soranou Ephessiou
115 27
Athens
Greece

Office: +302106597568

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Dr.rer.nat. Florian Dommert

Institute for Computational Physics
University Stuttgart

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70569 Stuttgart

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