[gmx-users] Fwd: Frequency dependent dielectric of water

[Bharat Sharma]

Hello Professor David,
I did not use Gromacs to calculate dipole autocorrelation function and I
did not set PME. I calculated molecular dipole from CP2K and I prepared
dipcorr.xvg file and used Gromacs's g_dielectric function for frequency
dependent dielectric.

In this case, what will be the epsRF?

I am trying to use g_dielectric function just to calculate frequecy
dependent dielectric using dipole ACF.

Thank you.

Bharat


On Mon, Jan 5, 2015 at 5:00 PM, David van der Spoel <spoel at xray.bmc.uu.se>
wrote:

> On 2015-01-05 20:56, Bharat Sharma wrote:
>
>> Hello Experts,
>> I am interested to calculate frequency dependent dielectric constant. I
>> prepared a dipcorr.xvg file and used g_dielectric function of gromacs to
>> calculate frequency dependent dielectric of water.
>>
>> I used this command.
>>
>> *g_dielectric_mpi -f dipcorr.xvg -eps0 95 -epsRF 1 -ffn exp_exp -bfit
>> 0.005
>> -eint 0.005 -fft*
>>
> why do you use epsRF 1? That means vacuum boundary conditions. If you used
> PME you should probably set 0.
>
> Note that you have to know what your are doing with this program and you
> may have to check the source code.
>
>
>> My model gives static dielectric of value 95.
>> However the problem is the intersection of real and imaginary dielectric
>> is
>> around 500 GHz which is not very realistic. The real value is around 10
>> GHz.
>>
>> I am wonder if I am doing something wrong on my command. Any suggestions
>> are appreciated.
>>
>> Thank you.
>>
>> Bharat
>>
>>
>
> --
> David van der Spoel, Ph.D., Professor of Biology
> Dept. of Cell & Molec. Biol., Uppsala University.
> Box 596, 75124 Uppsala, Sweden. Phone:  +46184714205.
> spoel at xray.bmc.uu.se    http://folding.bmc.uu.se
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