Mark:
Thanks for the rapid reply. I have made minor modifications to the
ffG43a1 force field (the one giving me these errors), but they are
really considerably minor. I have added an Azide molecule to the rtp
file (and corresponding atoms to the atp, etc.) and I have also added
an NME (similar to the NME in the charmm force field).
I decided to go ahead and untar the original 3.3 distribution, and go
back to the original ffG43a1 force field. This still did not solve the
problem. In fact, my small molecule is diglycine. If I run it with
neutral termini, I managed to get it to run through em, after simply
changing the box of water size (from 1.2 nm to 1.0 nm). This leads me
to believe it is a problem with the solvation. In fact, often times the
waters that exhibit infinite force are in the bulk (not even close to
the solute). This happens if I keep it solvated in spc, or change it to
spc/e.
The molecule is run through pdb2gmx_d with the following options: 0
(ffG43a1) -ter 0 (NH3+) 0 (COO-). With those options for a simple
diglycine, genbox_d should be able to solvate it fine. Also, pdb2gmx_d
shouldn't have trouble making a top file, either. From inspecting the
topology file, it looks perfectly fine. (two glycine residues, correct
atoms and types, good charges, includes all the correct itp files).
Finally, yes: the infinite force always occurs in step 0 with grid
searching.
My shell script only requires an initial pdb file to run, I can send it
along if it would help diagnose whether or not my version of gmx is
running correctly. (It is an unmodified source code, so it should be).
I just am unsure of what else could possibly be going wrong.
Thanks in advance,
Justin
Message: 6
Date: Fri, 20 Apr 2007 10:19:31 +1000
From: Mark Abraham <[EMAIL PROTECTED]>
Subject: Re: [gmx-users] Failed Energy Minimization
To: Discussion list for GROMACS users <[email protected]>
Message-ID: <[EMAIL PROTECTED]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Justin M. Shorb wrote:
Greetings:
I have been having trouble running any energy minimization with any
sort
of system. I have small polypeptides in water, and then large proteins
in water with the same error message:
No matter what run parameters I get, I always get ci = -2147483648.
Even
different systems. (This, I realize is simply numerically infinity).
If
I try running with ns_type = simple, the em runs until it hits around
35
and then says it didn't converge. Since I am running grompp_d -v, I
get
that there are certain atoms that have infinite potential. But,
depending on the system, the atom type (solvent or molecule) changes.
This suggests a problem with your force field and/or topology.
I have noted that previous posts have been answered with an
admonition:
"Find out which atoms are infinite force, and then fix it." I suppose
I
could go through, find the atoms and remove those waters that overlap,
but shouldn't this be taken into account by the genbox_d program? I
also
have tried to increase the vdw radii in the vdwradii.dat file to have
it
delete more waters. But, even after having 60 fewer waters around a 88
kD protein, the system still fails to energy minimize.
This suggests that the source of the problem isn't that these atoms
start life too close together, but maybe they're moving too close
together because of some other problem? (Unless the error is always
happening before the first EM step)
Given that this seems to be a common problem in solvating a system,
are
there better options (options for genbox??) than running the following
shell commands? The em.mdp file is also shown below.
That all seems fine.
Mark
_________________________________________________________________
Justin M. Shorb Phone: (608) 262-0483
Skinner Group [EMAIL PROTECTED]
University of Wisconsin-Madison, Department of Chemistry
1101 University Ave., Madison, WI, 53706
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