[gmx-users] Diagnosing + system blowing up

Shima Arasteh shima_arasteh2001 at yahoo.com
Sat Jul 28 17:16:07 CEST 2012

It's a little bit challenging problem I've got into! Certainly for me!

Thanks for your suggestions.


----- Original Message -----
From: Mark Abraham <Mark.Abraham at anu.edu.au>
To: Discussion list for GROMACS users <gmx-users at gromacs.org>
Sent: Saturday, July 28, 2012 7:15 PM
Subject: Re: [gmx-users] Diagnoding + system blowing up

On 28/07/2012 9:34 PM, Shima Arasteh wrote:
>   Hi all,
> My system has got BLOWING UP . I followed the protocol in http://www.gromacs.org/Documentation/Terminology/Blowing_Up and got as below:
> Step 1: If the crash is happening relatively early (within a few steps), set nstxout (or nstxtcout) to 1, capturing all possible frames.  Watch the resulting trajectory to see which atoms/residues/molecules become unstable first.
> I got this warning:
> Warning: 1-4 interaction between 5 and 18 at distance 2.003 which is larger than the 1-4 table size 2.000 nm

Classic symptom of blowing up, and much more so than all of the other problems you reported. Please get in the habit of reading all the output before reaching conclusions ;-)

> Step 2: Simplify the problem:
> If you have a new box of solvent, try minimizing and simulating a single molecule to see if the instability is due to some inherent problem with the  molecule's topology or if instead there are clashes in your starting configuration.
> I got this:
> Now there are 24 residues with 360 atoms
> Making bonds...
> Warning: Long Bond (1-18 = 0.357049 nm)

So you were ignoring warnings from pdb2gmx...? There's a lesson there - everything you've done after ignoring that was doomed to fail. It can be right to ignore a warning, but you should know why it is right. If your topology defines a bond between atoms that are 0.35nm apart in your starting configuration, then either your topology or configuration have a serious problem.

So satisfy yourself whether there should be such a bond in the topology, or whether the starting geometry is silly.

> Step 3: Monitor various components of the system's energy using g_energy.  If an intramolecular term is spiking, that may indicate improper bonded parameters, for example.
> The improper-dihedral plot is strange. It "goes up in first picoseconds" and then goes down slightly.

Sure, you probably have some inappropriate bond interaction, so something has to give. The thing that looks weird is not necessarily the cause of the problem, though...

> I think there is something wrong in dihedrals which I defined in .rtp file in the new residue. atom 18 is the H atom of formyl ( Formyl is as the N-terminus and  is connected to a Valine residue)

And atom 1 or 5 is...? Does that make sense?


> Now , what do I need to do? Going to the next step of diagnosing? or no? How can I fix the problem?
> Would you mind helping me please and give me suggestions?
> Thanks in advance.
> Sincerely,
> Shima

-- gmx-users mailing list    gmx-users at gromacs.org
* Only plain text messages are allowed!
* Please search the archive at http://www.gromacs.org/Support/Mailing_Lists/Search before posting!
* Please don't post (un)subscribe requests to the list. Use the www interface or send it to gmx-users-request at gromacs.org.
* Can't post? Read http://www.gromacs.org/Support/Mailing_Lists

More information about the gromacs.org_gmx-users mailing list