From: Stéphane Téletchéa <[EMAIL PROTECTED]>
Reply-To: Discussion list for GROMACS users <gmx-users@gromacs.org>
To: Discussion list for GROMACS users <gmx-users@gromacs.org>
Subject: Re: [gmx-users] Very large fluctuations in dg/dl
Date: Wed, 09 May 2007 11:11:06 +0200
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
What matters is not epsilon_rf, but 1/epsilon_rf.
Anything above roughly 20 does not make a significant difference any more.
Using 54 or 61 or infinity will not give measurable differences
in any property of the system, except for the fluctuation of the system
dipole.
Berk.
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