BSE

[fadoua]

Hi
I would to know if I can calculate BSE (yambo -o b -b -y h -p p) without the first calculation of self consistent (yambo -g n -p p).
Thanks in advance

[Daniele Varsano]

Dear Fadoua,
please fill you signature with your complete affiliation. This is a rule of the forum.
The BSE calculation requires quasi-particle energies, usually calculated within GW framework.
Anyway in some case, depending on your system, the QP correction is just an opening of the gap and you can take into account by shifting upward your conduction bands.
you can skip the GW calculation assigning the QP correction via a scissor operator. The value of the correction can be taken from a photoemission experiments or from previous calculations taken from literature.
In order to do that you can use the variable:

Code: Select all

%KfnQP_E				
0.000000|1.000000|1.000000|		#	(EXTQP)(BSK)(BSS)	 E parameters (c/v)
%

these three numbers are:
scissor | cond. stretching | val. stretching

with scissor is the QP correction to apply to the Kohn Sham conduction energies. The other two numbers apply a stretching to the QP energies with respect the Kohn-Sham. Leaving the unity value only a scissor is applied.

Hope it helps,

Daniele

PS: From the command line you posted you are using an old version of yambo (3.3). I suggest you to switch to the new one (3.4.1). If you do that, please see in the documentation the new commands.

[fadoua]

Dr Daniele
I understand now, Thank you very much for your clear response

[Daniele Varsano]

Dear Fadoua,
please, fill your signature with your affiliation.

Thanks,
Daniele

[fadoua]

Dr Daniele
Plz I have another question, I have already installed yambo 3.4.1, But I didn't know if this order "yambo -c -o b -b -k sex -y d" give us GW-BSE.
I work in 2D material, if I use this order "yambo -o b -k sex -b -y d -V qp" I found that excitation energy is higher then GW gap energy.
Thank you for your help

[Daniele Varsano]

Dear Fadwa,
reading carefully the report file you should be able to understand what yambo is exactly doing, and the differences
between the two calculations. The order used to setup the input file should not make differences.
Anyway , have a look to the manual:
http://www.yambo-code.org/input_file/ya ... /index.php

The differences between the two input file is that in the first case you are considering a cutoff interaction.
Of course, then it depends on the value of you input variables. Note that this is a BSE calculation and not a GW-BSE calculation.

Best,
Daniele