[gmx-users] want to calculate pressure from virial

[anirban polley]

Dear Sir,
           I want to calculate virial, hence pressure.
PV=NKT-1/3 * < sum of (r * f)>
          where r is displacement and f is internal force.  Now, how can I
proceed?
1. g_traj -f name.trr -af gives me force and each velocity with time?
Now, question, is the force given in data is only due to internal force or
total force on each atom?
Am I right if I use this force and position of the atom to calculate virial.

2. If I am wrong, then please tell me how I can calculate Virial, and hence
pressure.
3. I saw that g_energy -f name.edr -vis gives pressure, virial and all the
stuffs. I want to know that how I can calculate it myself.
4. Can you tell me how I can calculate pressure change with z - axis where I
am simulating Bilayer Membrane.
Thanking You,
Anirban
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