[gmx-users] Very large fluctuations in dg/dl

[Stéphane Téletchéa]

Patrick Fuchs a écrit :
> Hi Gromacs users,
> I have a few questions related to solvation free energy calculation via
> thermodynamic integration.

> #ifdef FLEX_SPC
> #include "flexspc.itp"
> #else
> #include "spc.itp"
> #endif

> coulombtype            = generalized-reaction-field
> rcoulomb               = 1.4
> rvdw                   = 1.4
> epsilon_rf             = 54.0

I cannot state for other parameters, but i'm surprised for the 
(relatively?) low value for epsilon_rf used here.

For instance in Geerke and van Gunsteren (ChempPhysChem 2006, 7, 
674-678), the value used for reaction-field (not generalized) is 61 for 
SPC water (referring to Heinz, van Gunsteren & Hunenberger, J Chem Phys 
2001, 115, p1125-1136).

Is this value a special case for 'generalized-reaction-field' ?

Thanks in advance for clarifications.

Stéphane

-- 
Stéphane Téletchéa, PhD.                  http://www.steletch.org
Unité Mathématique Informatique et Génome http://migale.jouy.inra.fr/mig
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