[gmx-users] dielectric constant

[David]

On Sat, 2003-06-14 at 09:17, s8026264 wrote:
> Dear All
> 
> 
> I am confuse.Buecuse you suggest a value for dielectric constant of SPC when
> 
> We use reaction field or generalized reactiom field  method (epsilon_r = 78 ) 
> 
this is a scientific question: do you want to surround your SPC water
with more SPC water or with "real" water?

Apart from answering that question, the difference is almost negligable.
Just try it and see, that's the best way to get a felling for these
things. Do a 1 ns simulation with both epsrf and compute properties like
dielectric constant etc. See also my paper:
@Article{Spoel98a,
  author        = {D. van der Spoel and P. J. van Maaren and H. J. C.
                  Berendsen},
  title         = {A systematic study of water models for molecular
                  simulation},
  year          = 1998,
  journal       = BTjcp,
  volume        = 108,
  pages         = {10220-10230}
}
 


> but I know about a paper that pepole found another value for dielectric 
> 
> constant of SPC.This valus is 54.
> 
> This paper and its abs. is :
> 
> Consistent dielectric properties of the simple point charge and extended
> simple point charge water models at 277 and 300 K
> 
> Paul E. Smith and Wilfred F. van Gunsteren Department of Physical Chemistry,
> Swiss Federal Institute of Technology Zürich, ETH-Zentrum, 8092 Zürich,
> Switzerland
> 
> (Received 14 September 1993; accepted 8 November 1993)
> 
> The dielectric constants (epsilon) of the simple point charge (SPC) and
> extended simple point charge (SPC/E) models of liquid water have been
> determined at 277 and 300 K using a reaction field (epsilonRF) treatment for
> the long-range electrostatic interaction. Consistent dielectric constants are
> obtained by using statistical mechanical perturbation theory, such that the
> properties of the system correspond to epsilonRF=epsilon, and are therefore
> representative of a true infinite system. The dielectric constants of SPC were
> determined to be 55.8 and 54.0 at 277 and 300 K, respectively, while the
> dielectric constants of SPC/E were 68.5 and 62.3 at 277 and 300 K,
> respectively. The Journal of Chemical Physics is copyrighted by The American
> Institute of Physics. 
> 
> 
> 
> 
> 
> Sincerely yours
> 
> 
> Mojtaba Alaei
> 
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-- 
Groeten, David.
________________________________________________________________________
Dr. David van der Spoel, 	Dept. of Cell and Molecular Biology
Husargatan 3, Box 596,  	75124 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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