[Pw_forum] absorption spectrum &dielectric constant of turboTDDFT

[Manu Hegde]

Hi Dario,
Thank you very much. I have done some calculations for UV-Vis (see
attached) and it is no where matching my experimental results in case of
bcc-In2O3. Is it due to pseudopotential (I have used PBE USPP)?. Also I am
unable to BZ sampling on k-mesh and TDDFT shown me an error.

Regards,
Manu
(University of Waterloo)

On Wed, Jul 20, 2016 at 8:09 PM, dario rocca <roccad at gmail.com> wrote:

> Dear Manu,
> You can simply extract it with the command
> $ grep "S(E)" prefix.plot_chi.dat  > file_for_plot
> and use your favorite program to plot it.
> Best,
> Dario
>
> On Wed, Jul 20, 2016 at 10:49 AM, Manu Hegde <mhegde at uwaterloo.ca> wrote:
>
>> Hello Dario,
>>
>> I have done the similar calculations, it went well, after running
>> turbo_spectrum.x  Do you have any code to extract S(E) or I have to do it
>> manually?
>>
>> Manu
>> (University of Waterloo)
>>
>> On Tue, Jul 19, 2016 at 8:24 PM, dario rocca <roccad at gmail.com> wrote:
>>
>>> Dear SungHwan,
>>> please refer to
>>> http://arxiv.org/pdf/1402.0486.pdf
>>> and
>>>
>>> http://urania.sissa.it/xmlui/bitstream/handle/1963/5797/turboTDDFT-CPC.pdf?sequence=1
>>> for more details.
>>>
>>> In the output of the postprocessing chi_1_1 is the xx component of the
>>> dynamical polarizability, chi_1_2 the xy component, etc.
>>> Often chi is indicated as \alpha in the papers.
>>> Specifically you would have
>>>
>>> Component      energy of the perturbation      real part of
>>> chi                          imaginary
>>>                       (indicated either as E or \omega)
>>> chi_1_1=          0.000000000000000E+00     0.955769346791472E+01
>>> 0.000000000000000E+00
>>> .........
>>>
>>> As you correctly say the absorption spectrum is related to the imaginary
>>> part of the average of chi multiplied by E (the energy E is often
>>> indicated as \omega).
>>> This averaged quantity is contained in S(E). Specifically S(E) is the
>>> strength function defined as
>>> S(E)=2m/(\pi*e^2*\hbar) * E*Im[chi(E)], where chi has been averaged over
>>> the 3 spatial directions.
>>> This definition is convenient because S(E) satisfies the f-sum rule.
>>> So if you extract S(E) and plot it you will have the absorption spectrum.
>>> Let me know if it's still not clear
>>> Best,
>>> Dario
>>>
>>>
>>>
>>>
>>> On Tue, Jul 19, 2016 at 4:01 PM, SungHwan Choi <sunghwanchoi91 at gmail.com
>>> > wrote:
>>>
>>>>     hi, I am a newbie for turboTDDFT. Now, I ran a simple example. It
>>>> was assume. Now I have prefix.plot_chi.dat  file. then I don't know
>>>> how to generate absorption spectrum from that file and dielectric
>>>> constant values. As far as I understood, the absorption spectrum is
>>>> related to imaginary part of average \chi value. but in the file there are 9
>>>> values
>>>>          chi_1_1
>>>>          chi_2_1
>>>>          chi_3_1
>>>>          chi_1_2
>>>>          chi_2_2
>>>>          chi_3_2
>>>>          chi_1_3
>>>>          chi_2_3
>>>>          chi_3_3
>>>> This is 3*3*3 tensor. how do I get an absorption spectrum and dieletric
>>>> constant values? by the way S(E) means what?
>>>>
>>>> Sincerely
>>>> Sunghwan Choi
>>>>
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>>>
>>>
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>>
>>
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