[gmx-users] ionomer topolgy

[Justin Lemkul]

On 9/27/13 8:43 PM, Ehsan Sadeghi wrote:
> Thanks for your prompt response. I made the modifications on the aminoacids.rtp file in Gromacs/gromacs-4.6.3/share/top/gromos53a6.ff.
>
> I did not modify any force field. I thought I still can use the default force field in gromos; isn't it right?

Yes you did; you modified the Gromos96 53A6 force field.  There's nothing wrong 
with that; it's precisely what you wanted to do.  Also note that there is no 
such thing as a default force field.

> Here is the output from pdb2gmx. Thank you for your consideration.
>
> -----------------------------------
>
> Opening force field file /usr/local/gromacs/share/gromacs/top/gromos53a6.ff/aminoacids.r2b
> Reading nafion3.pdb...
> WARNING: all CONECT records are ignored
> Read 46 atoms
> Analyzing pdb file
> Splitting chemical chains based on TER records or chain id changing.
> There are 2 chains and 0 blocks of water and 0 residues with 46 atoms
>
>    chain  #res #atoms
>    1 'G'     1     24
>    2 'H'     1     22
>
>
> WARNING: there were 1 atoms with zero occupancy and 45 atoms with
>           occupancy unequal to one (out of 46 atoms). Check your pdb file.
>
> Opening force field file /usr/local/gromacs/share/gromacs/top/gromos53a6.ff/atomtypes.atp
> Atomtype 1
> Reading residue database... (gromos53a6)
> Opening force field file /usr/local/gromacs/share/gromacs/top/gromos53a6.ff/aminoacids.rtp
> Using default: not generating all possible dihedrals
> Using default: excluding 3 bonded neighbors
> Using default: generating 1,4 H--H interactions
> Using default: removing proper dihedrals found on the same bond as a proper dihedral
> Residue 108
> Sorting it all out...
> Opening force field file /usr/local/gromacs/share/gromacs/top/gromos53a6.ff/aminoacids.hdb
> Opening force field file /usr/local/gromacs/share/gromacs/top/gromos53a6.ff/aminoacids.n.tdb
> Opening force field file /usr/local/gromacs/share/gromacs/top/gromos53a6.ff/aminoacids.c.tdb
>
> Back Off! I just backed up topol.top to ./#topol.top.36#
> Processing chain 1 'G' (24 atoms, 1 residues)
> Warning: Starting residue LI0 in chain not identified as Protein/RNA/DNA.
> Problem with chain definition, or missing terminal residues.
> This chain does not appear to contain a recognized chain molecule.
> If this is incorrect, you can edit residuetypes.dat to modify the behavior.
> 8 out of 8 lines of specbond.dat converted successfully
>
> -------------------------------------------------------
> Program pdb2gmx, VERSION 4.6.3
> Source code file: /home/ehssad/Downloads/Gromacs/gromacs-4.6.3/src/kernel/resall.c, line: 642
>
> Fatal error:
> Residue 'LI' not found in residue topology database
> For more information and tips for troubleshooting, please check the GROMACS
> website at http://www.gromacs.org/Documentation/Errors
>

Now your problem is that the .pdb file is misformatted.  Your residue name 
columns are shifted, such that pdb2gmx thinks "LI" is the residue and "G" is the 
chain identifier.  PDB format is fixed; if you mess it up, the contents become 
unreadable (or severely misinterpreted).

-Justin

-- 
==================================================

Justin A. Lemkul, Ph.D.
Postdoctoral Fellow

Department of Pharmaceutical Sciences
School of Pharmacy
Health Sciences Facility II, Room 601
University of Maryland, Baltimore
20 Penn St.
Baltimore, MD 21201

jalemkul at outerbanks.umaryland.edu | (410) 706-7441

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