[Pw_forum] absorption spectrum &dielectric constant of turboTDDFT

[dario rocca]

Hi Manu,
The last release of the code does not allow for k-point sampling, that's
why you get an error message.
You would need to use a supercell. If you have done a gamma only
calculation for your system that's probably why you get a spectrum
that does not match at all experiments.
Additionally, the Bethe-Salpeter equation is considered the most accurate
method for bulk solids.
Best,
Dario

On Thu, Jul 21, 2016 at 9:42 AM, Manu Hegde <mhegde at uwaterloo.ca> wrote:

> 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
>>>>>
>>>>> _______________________________________________
>>>>> Pw_forum mailing list
>>>>> Pw_forum at pwscf.org
>>>>> http://pwscf.org/mailman/listinfo/pw_forum
>>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>> Pw_forum mailing list
>>>> Pw_forum at pwscf.org
>>>> http://pwscf.org/mailman/listinfo/pw_forum
>>>>
>>>
>>>
>>> _______________________________________________
>>> Pw_forum mailing list
>>> Pw_forum at pwscf.org
>>> http://pwscf.org/mailman/listinfo/pw_forum
>>>
>>
>>
>> _______________________________________________
>> Pw_forum mailing list
>> Pw_forum at pwscf.org
>> http://pwscf.org/mailman/listinfo/pw_forum
>>
>
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20160721/8c2f0379/attachment.html>