[gmx-users] limit on energygrp_table

Adrien Leygue adrien.leygue at gmail.com
Tue Oct 9 17:13:21 CEST 2007

Dear Gromacs users (and developpers)

I need to use a force field, derived from ab initio methods, for which
the non-bonded interactions between the different atom types is a
modified 3-parameters LJ potential.

As this kind of potential is not implemented within Gromacs I am using
fully tabulated user defined potentials V_i_j for the non bonded
interactions between atom types i and j. The problem is that I have
many different atomtypes (on the order of 20) and therefore I have to
input many groups in the energygrp_table field of my mdp file.

When I run grompp I have a message saying that there is a limit on the
(254 if I remember correctly) on the number of groups that I can have
in  the energygrp_table field.

-Is there a way to increase this limit (by changing a constant and
then recompile) ? or is it more complicated (from the value 254 one
could guess that there is some one one-byte optimization)

-If the above solution is not an option, is there a "simple" way to
modify the Gromacs source code to use these more advanced potentials
while keeping good performances.

-Any other suggestion?

Thank you for your help.


Adrien Leygue

Department of Materials Science and Engineering
School of Chemical Engineering
National Technical University of Athens
9 Heroon Polytechniou Street
Zografou Campus, Athens 157 80,
Tel/Fax: +30210 772-3112

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