[gmx-developers] calculating dielectric constant

David van der Spoel spoel at xray.bmc.uu.se
Tue Nov 14 14:45:36 CET 2006

Qiao Baofu wrote:
> Hi all developers,
> I have posted this problem on the gmx-user list. David gave me some 
> suggestions, but the problem has not been solved completely.
> I simulated an ionic liquid [mmimCl], 981 molecules for 1.5 ns, every 5 
> time steps saved.  In the .mdp file, I used PME:{ coulombtype  = pme; 
> epsilon-r = 1}, the simulation temperatuer is 425K.
> Then I used  "g_dipoles -temp 425 -f -s -enx" to calculate the the 
> dielectric constant, the result is: Epsilon = 826.496. I checked the 
> epsilon.xvg, in which the result is converged to some extent with some 
> fluctuations at the end.  I think the result is too big. Even though I 
> have no exerimental data for [mmimCl] at hand, I have some reported data 
> of some other ionic liquids, 10-20.
> Is there anyone who can give some suggestions? Great thx!
Do you mean the other liquids have dielectric constant 10-20?
Or do you have 10-20 data poinst for other liquids.

Either way, try one of the other liquids to test it.

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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