Dear Eudes,
You need to technically make it 1 "big molecule". As long as there
are no bonds specified between molecule A and B. The big molecule
will behave as if there are two molecules in it. I do it to dock
small molecules to proteins.
Steps running Gromacs 3.3.3:
1) Combine molecules A and B into a big structure file (i.e. pdb or
gro).
2) Edit this file, so that they are the same chain.
3) run pdb2gmx
4) Change all the residue names to MOL and change Protein_A to MOL in
the top and pdb files.
5) Make sure that there is no bonds between molecule A and B in the
top file. There probably won't be, but it is good to check anyway.
5) run grompp to check this file to see if it is acceptable to gromacs.
6) add distance restraints after the improper dihedrals. If you put
it anywhere else, it will not work.
7) run grompp again to check this file to see if it is acceptable to
gromacs
Other advise:
1) I would roughly dock the molecules together, so that you don't have
to have such a large water box.
2) I would experiment with force constants and time constants for the
distance restraints. A useful article is:
Torda, A. E., Scheek, R. M., and Gunsteren, W. F. v. (1989) Time-
dependent distance restraints in molecular dynamics simulations, Chem.
Phys. Lett. 157, 289-294.
I hope that helps.
On Nov 15, 2008, at 3:58 AM, Eudes Fileti wrote:
Dear gmx-users, I need to use constraints between two
polyatomic molecules in order to calculate PMF using free energy code.
Can anybody help me to use these constraints over two different
molecules?
I ve already read something in the forum but not helped me enough.
(see http://www.gromacs.org/pipermail/gmx-users/2006-February/020049.html)
.
bests
eef
_______________________________________
Eudes Eterno Fileti
Centro de Ciências Naturais e Humanas
Universidade Federal do ABC
Rua Santa Adélia, 166 - Bloco B, Sala 1048
09210-170 Santo André - SP Brasil
+55.11.4437-8408
skype: eefileti
http://cromo.ufabc.edu.br/~fileti/
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