[gmx-users] Generalized-Reaction-Field; epsilon_r

David spoel at xray.bmc.uu.se
Wed Dec 18 07:46:08 CET 2002

On Wed, 2002-12-18 at 05:49, Dr. Y. U. Sasidhar wrote:
> *Generalized-Reaction-Field*
>     Generalized reaction field with Coulomb cut-off *rcoulomb*, where
>     *rcoulomb* >= *rvdw* >= *rlist*. The dielectric constant beyond the
>     cut-off is *epsilon_r*.
>     What are the values to be used for epsilon_r consistent with spc and
>     tip3p water models ?
>     I remember reading recently in a paper  that for tip3p you need to
>     use epsilon of 54, not 80.
The rationale behind that it would seem, is that you'd have more
TIP3P/SPC beyond the cut-off, rather than more water. Although such a
choice can be defended, there is no compelling physical argument for it.
Furthermore the difference is small. I prefer 80, but then I stopped
using RF, and use PME only.

Groeten, David.
Dr. David van der Spoel, 	Biomedical center, Dept. of Biochemistry
Husargatan 3, Box 576,  	75123 Uppsala, Sweden
phone:	46 18 471 4205		fax: 46 18 511 755
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://xray.bmc.uu.se/~spoel

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