## Imaginary part of SHG calculation

Questions and doubts about features of non linear optic in Yambo (yamb_nl)

Moderators: Davide Sangalli, claudio, myrta gruning

pangrt
Posts: 30
Joined: Thu Jun 18, 2020 1:38 pm

### Imaginary part of SHG calculation

Dear developers,
I am running SHG with Yambo and got the SHG chi, and how could I obtain the imaginary part of the dielectric constant at both
ω/2 and ω? (As in attached, the red solid and dashed lines)

Thanks!

Rongtian
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RongTianPang, Inner Mongolia University, Hohhot, China

lyzhao
Posts: 51
Joined: Tue May 31, 2016 8:02 am

### Re: Imaginary part of SHG calculation

Do you mean the imaginary part of the dielectric constant or SHG?
The dielectric constant is linear optical paramater and not SHG.
Youzhao Lan
College of Chemistry and Materials Science,
Zhejiang Normal University,
Jinhua, Zhejiang, China.
HomePage: http://blog.sciencenet.cn/u/lyzhao

pangrt
Posts: 30
Joined: Thu Jun 18, 2020 1:38 pm

### Re: Imaginary part of SHG calculation

Dear Zhao,
I think it is the imaginary part of the dielectric. How to obtain the dielectric constant at ω/2?

Thanks!

Rongtian
RongTianPang, Inner Mongolia University, Hohhot, China

lyzhao
Posts: 51
Joined: Tue May 31, 2016 8:02 am

### Re: Imaginary part of SHG calculation

please see the first tutorial at http://www.attaccalite.com/lumen/tutorials.html.
Youzhao Lan
College of Chemistry and Materials Science,
Zhejiang Normal University,
Jinhua, Zhejiang, China.
HomePage: http://blog.sciencenet.cn/u/lyzhao

pangrt
Posts: 30
Joined: Thu Jun 18, 2020 1:38 pm

### Re: Imaginary part of SHG calculation

I notice that just an abs. of ω instead of ω/2?

Thanks!
Rongtian
RongTianPang, Inner Mongolia University, Hohhot, China

AmberLee123
Posts: 35
Joined: Sun Jul 26, 2020 7:00 am
Location: Xiamen, Fujian, China

### Re: Imaginary part of SHG calculation

I think the abs. of ω/2 is just to extend the abs. of ω in the picture, ie. f(x/2) compared with f(x).
So there is no specially abs. of ω/2 in the output file from yambo. We just read abs. ω and then recalculate it.

Best.
Sincerely,
Dr. Guoyu Yang
Lecturer
Jimei Univ, School of Science, Digital Fujian Big Data Modeling and Intelligent Computing Institute
185 Yinjiang Rd.,
Jimei District, Xiamen,361021
Fujian, China
E-mail: 201961000100@jmu.edu.cn

claudio
Posts: 468
Joined: Tue Mar 31, 2009 11:33 pm
Location: Marseille
Contact:

### Re: Imaginary part of SHG calculation

Dear Rongtian

once you have the imaginary part of the dielectric constant, just plot it with the argument divided by two
for example in python:

plt.plot(EPS[:,0]/2., EPS[:,1],color="red", linewidth=3.0, linestyle="-", label="$\epsilon_2(\omega/2)$")
plt.plot(EPS[:,0], EPS[:,1],color="red", linewidth=3.0, linestyle="--",label="$\epsilon_2(\omega)$")

best
Claudio
Claudio Attaccalite
[CNRS/ Aix-Marseille Université/ CINaM laborarory / TSN department
Campus de Luminy – Case 913
13288 MARSEILLE Cedex 09
web site: http://www.attaccalite.com