[gmx-users] calculating dielectric constant

David van der Spoel spoel at xray.bmc.uu.se
Mon Nov 13 18:42:06 CET 2006

Qiao Baofu wrote:
> Hi all,
> I have some question about calculating dielectric constant:
> 1. From the manual, it seems that there are two methods to calculate the 
> dielectric constant: a. use g_dipoles -temp 400 -f -s directly, b) use 
> g_dipoles -nonormalize -corr total  -c dipcorr.xvg, then g_dielectric -f 
> dipcorr.xvg -o epsw.xvg. (Please correct me if the commandlines are 
> wrong). Thus I want to know the difference between them.

g_dielectric does another analyis. You want to run g_dipoles either with 
the -enx flag or with a trajectory.

> 2. If I want to calculate the dielectric constant, must I use the 
> Reaction Field in the couloumbtype? Now I have some results from PME. 
> Can I use these results directly to calculate the dielectric constant?

PME is fine. You have to supply the right dielectric constant to the 
program (though the default of 0 == infinity) is what most people use.

> Thanks very much in advances!
> Sincerely yours,
> Baofu Qiao
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David van der Spoel, PhD, Assoc. Prof., Molecular Biophysics group,
Dept. of Cell and Molecular Biology, Uppsala University.
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://folding.bmc.uu.se

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