Asking for help about the relationships bwtween alpla_2D(w) and alpha=-X/q^2

You can find here problems arising when using old releases of Yambo (< 5.0). Issues as parallelization strategy, performance issues and other technical aspects.

Moderators: Davide Sangalli, andrea.ferretti, myrta gruning, andrea marini, Daniele Varsano, Conor Hogan

Locked
Luo Yan
Posts: 31
Joined: Fri Jun 18, 2021 10:10 am
Location: Chengdu

Asking for help about the relationships bwtween alpla_2D(w) and alpha=-X/q^2

Post by Luo Yan » Thu Jun 09, 2022 6:38 am

In official website tutorial http://www.yambo-code.org/wiki/index.ph ... al_systems, it shows that “For a 2D system, the macroscopic polarizability (called here 'o-2D_WR_WC.alpha_q1_diago_bse') which is a well defined quantity strictly related to optical conductivity, or absorbance, is defined as attachment below” However, I find some topics show that "including the coulomb cutoff yambo print in output alpha defined as alpha=-X/q^2 where X is the response function."
Question 1: What's the relationship between two equations ?? I can't find more detailed derivation process about them, especially for the equation in the attachment below .
Question 2: Is the imaginary part of the GW and BSE polarizabilities obtained from "o-2D_WR_WC.alpha_q1_diago_bse" obtained via dielectric function Epsilon ε(q) = 1 + 2πα_2D|q|[PHYS. REV. B 84, 085406 (2011)] ? If not, how can I obtain the imaginary part of dielectric function in a 2D system ? If yes, the q tends to be 0, and the Epsilon is alway 1 ?
Thanks for your attentions. Best wish to you !
You do not have the required permissions to view the files attached to this post.
Luo Yan
Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China

lyzhao
Posts: 40
Joined: Tue May 31, 2016 8:02 am

Re: Asking for help about the relationships bwtween alpla_2D(w) and alpha=-X/q^2

Post by lyzhao » Thu Jun 09, 2022 6:58 am

Dear Luo,
The following posts should be helpful for you.
Real part of the dielectric function is absolutely one
viewtopic.php?t=1663&sid=10bd0adae13efd ... 5806ef1c30
Real part of the dielectric function
viewtopic.php?t=1858
Bethe salpether diago/inversion output
viewtopic.php?t=1715

Best regards.
Youzhao Lan
College of Chemistry and Materials Science,
Zhejiang Normal University,
Jinhua, Zhejiang, China.
HomePage: http://blog.sciencenet.cn/u/lyzhao

Luo Yan
Posts: 31
Joined: Fri Jun 18, 2021 10:10 am
Location: Chengdu

Re: Asking for help about the relationships bwtween alpla_2D(w) and alpha=-X/q^2

Post by Luo Yan » Thu Jun 09, 2022 9:42 am

Dear Lan,
I am very grateful for your quick reply. I will study these files.
Looking forward to further discussions with you!
Thank you once again.
Luo Yan
Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China

User avatar
Daniele Varsano
Posts: 3773
Joined: Tue Mar 17, 2009 2:23 pm
Contact:

Re: Asking for help about the relationships bwtween alpla_2D(w) and alpha=-X/q^2

Post by Daniele Varsano » Thu Jun 09, 2022 12:12 pm

Dear Luo,
If not, how can I obtain the imaginary part of the dielectric function in a 2D system? If yes, the q tends to be 0, and the Epsilon is alway 1 ?
Yes, the dielectric function behaves as you say, having a supercell with increasing vacuum to isolate the system, you are simulating a layered system with the interlayer distance increasing and in the limit, you obtain the eps of vacuum.

You can anyway define an eps_2d from the alpha_2d (see e.g. Rasmussen et al. PHYSICAL REVIEW B 94, 155406 (2016), Eq. 6 and text above where alpha_2d is defined).
In Yambo, alpha_2d is calculated in that way propto -X/q^2.
Alternatively you can evaluate it by discarding the coulomb cutoff potential and extracting it from Eq. 16 of PHYSICAL REVIEW B 84, 085406 (2011) you were mentioning, performing different calculations with increasing vacuum .

Best,
Daniele
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/

Luo Yan
Posts: 31
Joined: Fri Jun 18, 2021 10:10 am
Location: Chengdu

Re: Asking for help about the relationships bwtween alpla_2D(w) and alpha=-X/q^2

Post by Luo Yan » Fri Jun 10, 2022 9:07 am

Dear Daniele,
Thanks four your detailed helps. Could you offer me more deduced informations about the response function X used in Yambo ?
Thank you !
Luo Yan
Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China

User avatar
Daniele Varsano
Posts: 3773
Joined: Tue Mar 17, 2009 2:23 pm
Contact:

Re: Asking for help about the relationships bwtween alpla_2D(w) and alpha=-X/q^2

Post by Daniele Varsano » Sat Jun 11, 2022 9:28 am

Dear Luo,

you can have a look at the yambo cheatsheet to look on how X and many other quantities are calculated.

http://www.yambo-code.org/wiki/index.ph ... heatsheets


Best,
Daniele
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/

Locked