[gmx-users] Fourier transformation of dipole autocorrelation function

Florian Dommert dommert at icp.uni-stuttgart.de
Wed Jan 19 09:53:44 CET 2011

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On 01/18/2011 10:56 PM, Mark Abraham wrote:
> On 19/01/2011 8:19 AM, Nilesh Dhumal wrote:
>> Then didn't mentioned what they calculated Fourier transformation of
>> dipole
>> autocorrelation. They have given the equations and theory in papers.
> I'd ask them - it's outside the scope of GROMACS. Some tool like Matlab,
> Mathematica or R is probably best.
> Mark


 calculating dipole moments of systems containing charged molecules is
not straightforward, especially for ionic liquids. To obtain the
frequency dependent dielectric constant you have to perform a FT of the
autocorrelation function for the total dipole moment. However due to the
PBC, the function of the total dipole moment in time is not continuous
and cannot be derived by simple averaging over the time frames. C.
Schroeder from the group of O. Steinhauser has calculated IL spectra and
I would take a look at their published literature.

>> Nilesh
>> On Tue, January 18, 2011 3:52 pm, Mark Abraham wrote:
>>> On 19/01/2011 6:40 AM, Nilesh Dhumal wrote:
>>>> Hello,
>>>> I am trying to calculate the vibrational spectra for my system which
>>>> consist of an ion-pair of ionic liquid (cation and anion) and 254 water
>>>> molecules. I am following the procedure from J. Phys. Chem. A. 2004,
>>>> 108(50), 11056 and Macromolecules 1192, 25, 4605.
>>>> The vibrational spectra is calculated by Fourier transforming the
>>>> dipole
>>>>   moment autocorrelation function.
>>>> I can calculate the dipole autocorrelation function using g_dipole.
>>> Did you start by reading g_dipoles -h?
>>>> How can I calculate the Fourier transformation of dipole
>>>> autocorrelation
>>> How did those authors do it?
>>> Mark
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- -- 
Florian Dommert

Institute for Computational Physics

University Stuttgart

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