How it works the Quasi-Particle shift?

[javad]

Dear developers

I'm trying to do a calculation of optics with a GW-shift,
I have done

yambo -o c -V QP

I got in the input

% XfnQP_E
0.000000 | 1.000000 | 1.000000 | # [EXTQP Xd] E parameters (c/v) eV|adim|adim
%

I understood that the first number is the correction to the gap, what are the other two numbers? and how can I use them?

with best regards
Javad Exirifard

[Daniele Varsano]

Dear Javad,

I'm trying to do a calculation of optics with a GW-shift,
I have done

yambo -o c -V QP

OK, but be careful, if you do a linear response calcualtion (RPA) applying a QP shift it is not totally consistent, the QP correction is meant for a BS calculation.

I got in the input

% XfnQP_E
0.000000 | 1.000000 | 1.000000 | # [EXTQP Xd] E parameters (c/v) eV|adim|adim
%

I understood that the first number is the correction to the gap, what are the other two numbers? and how can I use them?

The other two variable refers to the slope of the valence/conductions QP energies (coming from a GW calculations for isntances) with respect the KS energies. You can fit them by plotting E_qp vs E_lda. Sometimes beside the QP shift you have a different slope for valence and conduction energies. Considering

Code: Select all

QP_shift |1 |1 

you apply only the shift and it is the so called scissor operator approximation.
See here for a description:
If you cannot apply a simple shift (as for instances in many molecules), you need to calculate the QP energies you need and apply them using the Qpdb variable with the syntax:

Code: Select all

"E < example/(n)db.QP" 

here (n) is if you linked with the netcdf libraries.

Hope it helps,
Best,
Daniele