## optical conductivity

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.
Weiqing Zhou
Posts: 48
Joined: Thu Sep 06, 2018 7:57 am
Location: Wuhan University

### optical conductivity

Hi all,

I want to whether there is a way to get conductivity /sigma from Yambo directly.
If answer is no, I can finish it by the relation between dielectric function and conductivity. Before that, I must know the unit of dielectric function in o. file. can anyone tell me this ?

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

Daniele Varsano
Posts: 2723
Joined: Tue Mar 17, 2009 2:23 pm
Contact:

### Re: optical conductivity

Dear Weiqing,
no, there is not the possibility to have the conductivity as an output.
Note that the dielectric function by its definition is a mere number so it has not unit.
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/

Weiqing Zhou
Posts: 48
Joined: Thu Sep 06, 2018 7:57 am
Location: Wuhan University

### Re: optical conductivity

Dear Daniele,
that the dielectric function by its definition is a mere number so it has not unit.
Actully, vaccum dielectric function has well-defined unit [(pi*e^2)/2h].
Can I understand in this way? In Yambo, the output of dielectric function is permittivity, the ratio of dielectric function to that of vaccum.

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

Daniele Varsano
Posts: 2723
Joined: Tue Mar 17, 2009 2:23 pm
Contact:

### Re: optical conductivity

Dear Weiqing,
Can I understand in this way? In Yambo, the output of dielectric function is permittivity, the ratio of dielectric function to that of vaccum.
yes, it is as you said.

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/

Weiqing Zhou
Posts: 48
Joined: Thu Sep 06, 2018 7:57 am
Location: Wuhan University

### Re: optical conductivity

Dear Daniele,

I want to make sure the dielectric function from Yambo is in the unit of vacuum dielectric function $\epsilon_{0}$, which can be rewritten as
$\epsilon_{0}=\frac {e^{2}}{2\alpha h c}$ where $e$ is the elementary charge, $h$ is exact Planck constant, $\alpha$ is the dimensionless fine-structure constant and $c$ is the light velocity. No any prefactor else?

I want to get conductivity, and a well-fined unit is very important. Now the problem I face is the conductivity I convert from Yambo is two orders of magnitude smaller than that of other articles, while other details are all same.

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

Daniele Varsano
Posts: 2723
Joined: Tue Mar 17, 2009 2:23 pm
Contact:

### Re: optical conductivity

Dear Weiqing,
yes, the dielectric function is defined as
eps^-1=1+vX
where v is the Coulomb potential and X is the response function. In vacuum it is exactly 1.
If you are dealing with non-3D bulk systems (e.g. 2D systems etc.) issues related to the volume of the supercell arise.

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/