[gmx-users] Calculating osmotic coefficient through virial/kinetic terms: what is the handy way?

Vries, de, H.W. h.w.de.vries.6 at student.rug.nl
Fri Dec 9 13:17:11 CET 2016

Dear all,

I am trying to find the osmotic coefficient of a set of ions in an implicit
solvent system in gromacs 4.5.3. I have found multiple papers reporting an
expression of the form:

Osm. coefficient = 1- (Virial/Ekinetic).

I can find in the manual (appendix B) how the single sum virial is computed
(incl. PBC), but I don't completely understand how to extract the virial
energy of my system out of my simulation data. g_energy only seems to
return vir-XX to vir-ZZ terms, which indicate the tensor components.

Is there a handy option that I'm missing that computes the complete virial
term of my system, or do I have to manually sum all components?


Henry de Vries

Henry de Vries
Student Topmaster Nanoscience
ZIAM // University of Groningen, NL

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