From: "Adrien Leygue" <[EMAIL PROTECTED]>
Reply-To: Discussion list for GROMACS users <gmx-users@gromacs.org>
To: gmx-users@gromacs.org
Subject: [gmx-users] limit on energygrp_table
Date: Tue, 9 Oct 2007 18:13:21 +0300
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)
This is indeed a on-byte optimization.
The group numbers are stored as uchars (include/types/atoms.h).
You could change this, then you also have to change 2 or more other files
for the io and communication of these numbers.
-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.
This depends on what combination rules you have for your parameters.
If you are lucky, you can use the buckingham 3-parameter setup
and modify the plain C buckingham innerloops to calculate your functional
form.
Berk.
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