[QE-users] q1, q2, q3 values for turbo_eels.x method

[Timrov Iurii]

Dear Vivek,


If your supercell is large enough, you can try to compute the absorption spectrum using the turbo_lanczos.x or turbo_davidson.x codes and using only one k point (k=0). For these codes you need to specify "K_POINTS {gamma}". k point grids different from k=0 are currently not supported by these codes.


If you do need to use k point grids, then yes you can try to use the turbo_eels.x code as a workaround (though originally this code was developed to model EELS spectra). Then you need to plot Im(eps), where eps is the dielectric function. For optical absorption, the transferred momentum is vanishing (q->0), so you can specify some small numbers for q1, q2, q3 (but not exactly zero, because this limit is not implemented). So you can try something like (note, the direction of q is not important):

   q1 = 0.001,
   q2 = 0.000,
   q3 = 0.000


Cheers,

Iurii


--
Dr. Iurii TIMROV
Postdoctoral Researcher
STI - IMX - THEOS and NCCR - MARVEL
Swiss Federal Institute of Technology Lausanne (EPFL)
CH-1015 Lausanne, Switzerland
+41 21 69 34 881
http://people.epfl.ch/265334
________________________________
From: users <users-bounces at lists.quantum-espresso.org> on behalf of Vivek Christhunathan <vivekppn at gmail.com>
Sent: Tuesday, August 18, 2020 4:19:52 PM
To: Quantum ESPRESSO users Forum
Subject: [QE-users] q1, q2, q3 values for turbo_eels.x method

Hi Everyone,

Greetings!!!

I am trying to do absorption spectrum calculation for anatase TiO2 which consist of 48 atoms (2x2x1 supercell) by using turbo_eels.x method. I have done scf calculation for this.
The default value for q1, q2, and q3 is 1. So, to get the correct output data for the calculation what value should I give for q1, q2, and q3 tags which are present in the turbo_eels.x.

Please find the attached files for the reference.

Your response is highly appreciated.

Thanks in advance.

Kind Regards,
Vivek C

__________________________________
Vivek Christhunathan
PhD researcher
Mechanical Engineering
College of Engineering and Informatics
Room 2053
Alice Perry Engineering Building
National University of Ireland Galway
Ireland
E-mail: v.christhunathan1 at nuigalway.ie<mailto:v.christhunathan1 at nuigalway.ie>
Phone: +353 899811181, +91 9600752742
[https://docs.google.com/uc?export=download&id=1oPtxd7PT5ljQRnuP-Gdf5upjiKPXk7Fz&revid=0B_S3ZLbRRu26NW1YallITFk1ZHMxaStQaUVoMjZ4M2NqcC9BPQ]
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