[gmx-users] how to simulate at a specific dielectric constant

[David van der Spoel]

Qiao Baofu wrote:
> Hi David,
> 
>     There is not a simulation parameter that you can change that will
>     influence the dielectric constant of your system. 
> 
> 
> I don't grasp this. If the system has two fluid, one as solute, another 
> as solvent. I had thought that I should change the value epsilon_r in 
> the .mdp file from the default 1 to some other value. Is it wrong?
> 
Yes. If you change epsilon_r the Coulomb interaction will be scaled but 
not the Van der Waals. Hence the balance of forces is disturbed and you 
system will implode (epsilon_r < 1) or explode (epsilon_r > 1). You are 
probably thinking of implicit solvent methds where this might apply, but 
these are not implemented in GROMACS.

-- 
David.
________________________________________________________________________
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
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++