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

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


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