[gmx-users] where are the forces?

Albert Solernou a.solernou at leeds.ac.uk
Thu Apr 2 18:19:02 CEST 2015

I am trying to get a trajectory that include forces... but I am not sure 
I am getting it. My .mdp file has the following lines:
  nstxout         = 500           ; save coordinates every 1.0 ps
  nstvout         = 500           ; save velocities every 1.0 ps
  nstenergy       = 500           ; save energies every 1.0 ps
  nstfout         = 500           ; save forces every 1.0 ps
  nstlog          = 500           ; update log file every 1.0 ps
but because the trajectory is saved in a .trr file... it is difficult to 
know whether the forces are there or not.

Therefore, I turn my .trr trajectory into .gro, to see what is in there:
  gmx trjconv -vel -force -s gmx.tpr -f gmx.trr -o gmx.gro
and I expect to see 9 numbers after every atom, but there are only 6... 
and when I "trjconv" using "-novel", then only 3 numbers are there.

So the question is: where are the forces? Were they saved at all?


   Dr Albert Solernou
   EPSRC Research Fellow,
   Department of Physics and Astronomy,
   University of Leeds

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