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Re^5: Can we calculate Frequency dependent dielectric constant of any sample?

Alex Granovsky

Dear Siddheshwar,

I'm sorry for misinterpreting your question.

The polarizability computed using TDHF/TDDFT is the electronic
polarizability. The only reason why it is not possible to enter
very small frequency values is that computed frequency-dependent
polarizability will in fact be virtually identical to the static one.
I can remove this check but this will be of little help to you.

Kind regards,

On Sat Jun 22 '13 10:27am, Siddheshwar Chopra wrote
>Dear Alex,
>Thats not exactly the answer for what I asked. I want to know what should be the values of FREQ(1) for frequencies corresponding to 1MHz to 20GHz. As I understood from the FIREFLY manual, I can only  set a minimum of 0.000001 a.u. which corresponds to around 10e11 Hz. Thats the concern to me.. This range means that I can set a minimum of 100Ghz or so.. Please help.

>n Sat Jun 22 '13 6:09am, Alex Granovsky wrote
>>Dear Siddheshwar,

>>you can specify up to 10 frequencies at once.
>>Set nfreq to 10 and provide desired values
>>in the freq array. It is recommended to set the
>>first frequency to zero and enlist frequencies
>>in ascending order. Note they are given in atomic
>>units so you need to convert your MHz or GHz values
>>to atomic units.

>>Hope this helps.

>>Kind regards,

>>On Wed Jun 19 '13 2:24pm, Siddheshwar Chopra wrote
>>>Dear Alex,
>>>Thank you for the information. As per your input file, I ran the program to find polarizability of a molecule. I wish to ask that is it possible to give the FREQ(n) array for a range of 1MHz to 20GHz? Is it possible to get this frequency range in FIREFLY?


>>>On Tue Jun 18 '13 8:02pm, Alex Granovsky wrote
>>>>Dear Siddheshwar,

>>>>dielectric constant is a macroscopic property.
>>>>At microscopic level, we can compute frequency-dependent
>>>>polarizabilities and hyper-polarizabilities. Having a certain
>>>>model of the macroscopic body one can relate a microscopic
>>>>properties such as polarizability to a dielectric constant.

>>>>Below please find a sample file with computation of
>>>>frequency-dependent polarizability for benzene molecule
>>>>using PBE0 density functional. In brief, this is done
>>>>using runtyp=TDHF and specifying some DFTTYP.
>>>>If no DFTTYP is given, then these are indeed classical
>>>>TDHF calculations, if DFTTYP is given then they in fact
>>>>become TDDFT computations.


 $TDHF NFREQ=2 FREQ(1)=0,0.1 $END
Dnh       6

CARBON      6.0     -0.698164472         1.209256337         0.000000000
HYDROGEN    1.0     -1.241338149         2.150060743         0.000000000

>>>>Kind regards,
>>>>Alex Granovsky
>>>>On Fri Jun 14 '13 11:00am, Siddheshwar Chopra wrote
>>>>>Dear Sir,
>>>>>I would be glad if you could throw some light on How to calculate the frequency dependent Dielectric constant using FIREFLY?? As far as I have read, DFPT is used to do the same... please help.


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