Dear Lamia,

but I don't know how to get the band gap value and how to plot the band structure of the system?

The band gap is contained in the o.qp as you have the GW correction, provided that you calculated the GW correction for the band and K point

where the gap appear.

In order to have the band structure through a path connecting high symmetry point you need to interpolate the QP energies: this is explained for instance

at the end of this GW tutorial:

http://www.yambo-code.org/wiki/index.ph ... rial:_h-BN Also, what's the information can I get it from it.

IN the o.qp essentially you have the output of your calculation, GW correction, exchange self energy contribution, correlation self energy contribution etc..

What information you can get from a GW calculation, I invite you to look at some textbook or review on the topic.

Here you can find links to lecture notes, reviews, book chapters etc.:

http://www.yambo-code.org/theory/lectures.phpBest,

Daniele