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

[Vries, de, H.W.]

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?


best,

Henry de Vries

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