## damping parameter

Deals with issues related to computation of optical spectra, in RPA (-o c) or by solving the Bethe-Salpeter equation (-o b). Includes local field effects, excitons, etc.

Moderators: Davide Sangalli, andrea marini, Conor Hogan, myrta gruning

### damping parameter

Hi all,

I find DmRnge setting has two parameters, min energy and max energy. And the damping grows linearly between them. I want to know:
1. what factors can affect damping in real material ? defect, temperature?
2. Why yambo make this design (min energy and max energy) ? Is damping expected to be bigger when photon energy increases ?

in ohter post, I find that real part of DrudeW is frequency of Drude plasmon and imaginary part is damping.
1. what factors can affect drude damping in real material ?
2. when I set real part of DrudeW 20 eV, I find results are good agreement with experimental result. I think 20 eV is too large. Is it possible that the frequency of Drude plasmon is 20 eV ?

Best,
Weiqing
Weiqing Zhou
Phd student
Wuhan University
Wuhan, Hubei, 430072
Weiqing Zhou

Posts: 45
Joined: Thu Sep 06, 2018 7:57 am
Location: Wuhan University

### Re: damping parameter

Dear Weiqing,
1. what factors can affect damping in real material ? defect, temperature?

In general, you have finite lifetime due to different interactions? The temperature (el-ph interaction) for sure contributes to it.
2. Why yambo make this design (min energy and max energy) ? Is damping expected to be bigger when photon energy increases ?

This is just an option provided by yambo, feel free to set them at the same value. Note that this is just "empirical damping".
1. what factors can affect Drude damping in real material ?

See point 1, there is damping as there is a finite lifetime.
2. when I set real part of DrudeW 20 eV, I find results are good agreement with experimental result. I think 20 eV is too large. Is it possible that the frequency of Drude plasmon is 20 eV ?

Do not know the system you are studying, anyway, this is a question not related with the code but with your research project and I think you need to discuss it with your colleagues/collaborators.
A practical way to estimate Drude parameter is to look at finite-q absorption spectra: fit with a Drude function and extrapolate the parameters to lim q->0.
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/

Daniele Varsano

Posts: 1972
Joined: Tue Mar 17, 2009 2:23 pm

### Re: damping parameter

Dear Daniele,

A practical way to estimate Drude parameter is to look at finite-q absorption spectra: fit with a Drude function and extrapolate the parameters to lim q->0.

Acutally, I don't understand this procedure. Because in other post (viewtopic.php?f=13&t=1541) where I mention
for finite q, Drude term makes no difference in dielectric function.

indeed, the Drude term takes into account the term coming for interband transitions in the limit q->0.
For finite q, interband transitions are correctly taken into account in the response function

How to "fit with a Drude function and extrapolate the parameters to lim q->0" ? Since I always have same dielectric function whatever I set DrudeWXd for finite-q. I am confused about this.

Best,
Weiqing
Weiqing Zhou
Phd student
Wuhan University
Wuhan, Hubei, 430072
Weiqing Zhou

Posts: 45
Joined: Thu Sep 06, 2018 7:57 am
Location: Wuhan University

### Re: damping parameter

Dear Weiqing,
indeed Drude is meant for q=0: a Drude function is added to non-interacting response. This is empirical and it depends on two parameters.
The way I do suggest is to calculate the response function for small q (all is calculated ab-inito taking into account all the possible transition and the Drude term does not affect the response),
you fit your ab-initio result, with a Drude like function and in this way, you can extract the parameters for small q and have an idea (or extrapolate) the parameters for the q->0 limit that will be
taken into account by the Drude term.. Of course, if you know the parameters from the literature or any other way you do not need it.

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/

Daniele Varsano

Posts: 1972
Joined: Tue Mar 17, 2009 2:23 pm

### Re: damping parameter

Dear Daniele,

For Drude term, I still have some confusions.
1. In yambo, is it possible to add more than one Drude modes into response function ?
2. If what I focus on is GW calculation instead of optical response, should I add Drude term into GW calculation?

Best,
Weiqing
Weiqing Zhou
Phd student
Wuhan University
Wuhan, Hubei, 430072
Weiqing Zhou

Posts: 45
Joined: Thu Sep 06, 2018 7:57 am
Location: Wuhan University

### Re: damping parameter

Dear Weiking,
1. In yambo, is it possible to add more than one Drude modes into response function ?

No, in Yambo there is just one plasmon frequency that can be set.
2. If what I focus on is GW calculation instead of optical response, should I add Drude term into GW calculation?

The Drude contribution can be considered for a full frequency calculation, I suppose. It is not allowed in the plasmon-pole approximation. Even if sometimes it can give reasonable results, the use of PP for a metal anyway is questionable.

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/

Daniele Varsano

Posts: 1972
Joined: Tue Mar 17, 2009 2:23 pm

### Re: damping parameter

Dear Daniele,

I want to know weather the Drude plasmon frequqency defined in Yambo is plasma frequency , which can be predicted by Eq. (5) in PHYSICAL REVIEW B 79, 125117 (2009).

Best,
Weiqing
Weiqing Zhou
Phd student
Wuhan University
Wuhan, Hubei, 430072
Weiqing Zhou

Posts: 45
Joined: Thu Sep 06, 2018 7:57 am
Location: Wuhan University

### electron phonon coupling supercell

Dear Yambo users
my name is Salah Alsmairat, I am PhD student, trying to calculate electron phonon coupling constant for Al super cell, 2*2*2.
I am doing that using DFT codes, quantum espresso for example but it is time consuming. can I use Yambo without the need for qe, or abinit , or any other code. Is it faster?
And could you please give me the steps in details to follow.
I am sorry , I dont know if this is the right place for the post, I am still new to forum.
Thanks
saaxx2

Posts: 2
Joined: Mon May 06, 2019 2:51 am

### Re: damping parameter

Dear Saaxx2,
I am sorry , I dont know if this is the right place for the post, I am still new to forum.

please sing your posts with your name and affiliation, this is a rule of the forum and you can do once for all by filling the signature in your user profile.
Next, please post your question in the right subforum, in this way it is easier to find for all the forum members.
can I use Yambo without the need for qe, or abinit , or any other code

Yambo is a many body code that needs a ground state as a starting point, so you need to calculate it using qe or abinit and next use the proper interface which come with the yambo suite.

In the yambo webpage you can find step by step tutorials on how to use yambo:
http://www.yambo-code.org/wiki/index.ph ... =Tutorials
http://www.yambo-code.org/tutorials/index.php
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/

Daniele Varsano

Posts: 1972
Joined: Tue Mar 17, 2009 2:23 pm