Thanks Dr Hess.
I didn't get an error message when using grompp, then I think I didn't have too
many exclusions.
I didn't know about using couple_type in this context before. If I get it
correctly, if I want to exclude all non-bonding interactions inside a protein
using couple_type, I must define it as follows in each mdp file for each
lambda: (I need to decouple all the non-bonding intra molecular interactions
for each lambdas):
couple_moltype=protein
couple_lambda0=none
couple_lambda1=none
couple-intramol=none
If this is right, I will test it for my system which has ~7000 protein atoms.
BTW I am still a little confused about the reported 1-4 energies while using
exclusions, could you please explain this?. For my smaller system I got zero SR
but non-zero 1-4 energies, even that the interactions between all the atoms
were excluded. If I remove the pairs in topology file I would get no 1-4 term
along with a different dV/dl value. So does it mean if I want to exclude all
the intramolecular interactions I have to remove pairs? (my system is frozen
and therefore I am not worried about the conformational change of the protein
and also I am mainly interested in dV/dl values, which in this case is related
to the electrostatic interaction of a residue with water as the charges on that
residue being turned off).
Regards,
Reza Salari
________________________________
From: Berk Hess <g...@hotmail.com>
To: Discussion list for GROMACS users <gmx-users@gromacs.org>
Sent: Thu, December 3, 2009 3:30:27 AM
Subject: RE: [gmx-users] Exclusions in topology file seem not working for big
systems
Hi,
If you really had too many exclusions you would get an error message.
So I just tested this.
I used the couple_moltype option to couple a 389 atom protein.
This generates exclusions between each protein atom and the 388 others.
All interactions are excluded correctly (and re-added as special 1-4's because
of the couple option).
So I don't understand what is going wrong in your case.
Berk
________________________________
Date: Wed, 2 Dec 2009 09:31:03 -0800
From: resa...@yahoo.com
Subject: Re: [gmx-users] Exclusions in topology file seem not working for big
systems
To: gmx-users@gromacs.org
Thanks for your response Dr van der Spoel.
Then there is a limit on the number of atoms that can be defined in the
exclusions section. My smaller system has 60 atoms and I used exclusions
successfully for that, so I guess the limit might be a little more than 32.
Regarding the use of energygrp_excl,it seems it does not work with PME. If I
define the protein in the energygrp_excl group, grompp gives me this warning:
Can not exclude the lattice Coulomb energy between energy groups
Which I think means some of electrostatics is not going to be excluded between
protein atoms. Is there a workaround for this? I think my last resort would be
to run a simulation first with PME and without exclusions, and then rerunning
it but this time by defining protein in the energygrp_excl and using cut-off
instead of PME. Then I guess I will be left with only protein-water
interactions.
Regards,
Reza Salari
________________________________
From: David van der Spoel <sp...@xray.bmc.uu.se>
To: Discussion list for GROMACS users <gmx-users@gromacs.org>
Sent: Wed, December 2, 2009 11:59:49 AM
Subject: Re: [gmx-users] Exclusions in topology file seem not working for big
systems
Reza Salari wrote:
> Hi All,
>
> I seem to have a hard time to use exclusions in topology file. I have a
> relatively big system (~400 aa) that I am trying to calculate the difference
> in desolvation energy (dA) upon turning off charges on a specific residue
> using thermodynamics integration method. The system is a complex of two
> proteins and is frozen inside the box (for my project I need it to be
> frozen).ยจ
You can have max 32 exclusions per atom AFAIK.
However you can use energy_group_excluisions in the mdp file.
>
> To calculate the desolvation energy, I need to exclude all the non-bonding
> interactions among protein atoms, then the dA that I get corresponds to the
> desolvation energy (and doesn't include the lost interactions between mutated
> residue and the rest of protein). I couldn't use energygrp_excl in mdp file
> since I am using PME. So I defined exclusions in topology file as follows
> (three-dot means that numbers continue to the last number):
>
> [ exclusions]
> 1 2 3 4 5 6 ... 6420
> 2 1 3 4 5 6 ... 6420
> 3 1 2 4 5 6 ... 6420
> ...
> ...
> 6420 1 2 3 ... 6419
>
> I used gmxdump to check that the exclusions were actually implemented, and it
> seems that they were.
>
> However when I use g_energy, I don't get zero energy for short range
> interactions. Here are the results of g_energy for simulations with and
> without exclusions:
>
> Coul-SR:Protein-Protein LJ-SR:Protein-Protein
> Coul-14:Protein-Protein LJ-14:Protein-Protein
> no exclusions -20277.6
> -13030.7
> 37023.9 7890.52
> using exclusions -16221.2
> -10332.9 37023.9
> 7890.52
>
>
> I did the same test with a small system (~6 residue) and I did get zero SR
> interactions. While the exclusions work for my small system, I don't know why
> they seem not working for my bigger system. Am I missing something here or is
> there something like an implicit limit for the number of atoms that can be
> defined in the exclusion section of topology file?
>
> I appreciate any hint or help.
>
> Regards,
> Reza Salari
>
-- David.
________________________________________________________________________
David van der Spoel, PhD, Professor of Biology
Dept. of Cell and Molecular Biology, Uppsala University.
Husargatan 3, Box 596, 75124 Uppsala, Sweden
phone: 46 18 471 4205 fax: 46 18 511 755
sp...@xray.bmc.uu.se sp...@gromacs.org http://folding.bmc.uu.se
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