[gmx-users] Re: DNA simulations

[Justin A. Lemkul]

On 7/9/12 4:07 PM, SatyaK wrote:
>   Hello,
>
>   I followed below steps using VMD and GROMACS but something went wrong in
> using GROMACS which I am not able to figure out. Appreciate your help.
>
>   1. editconf -f initialfile.pdb -o initialfile.gro -d 0.2
>   2. VMD: within 5 of nucleic
>               $sel writepdb initialfile_updated.pdb
>               $sel delete
>
>        (initialfile_updated.pdb has only those molecules that are at a
> distance of 5A)
>
>   3. I used GROMACS to convert back to .gro:editconf -f
> initialfile_updated.pdb -o initialfile_updated.gro -d 0.2
>
>   The coordinates in ininitialfile.gro and initialfile_updared.gro are
> different. I quite don't understand the reason for the same.

You are resetting the box by invoking the -d option with editconf.  If 
initialfile.gro had all the original atoms and initialfile_updated.gro has 
significantly fewer (due to the selection made in VMD), then the size associated 
with the system is much smaller.  Using -d re-centers the system within the 
defined box, thus shifting the coordinates.

-Justin

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

Justin A. Lemkul, Ph.D.
Research Scientist
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin

========================================