how to get Infromation about QP band gap from BSE spectrum

[Bramhachari Khamari]

Dear Sir,
I have obtained GW+BSE spectrum of a material. I have also done the real time BSE calculation. I would like to know the information of quasiparticle (QP) gap from BSE spectrum obtained using real time simulation (yambo_rt). I mean to say that If the intensity of the pulse is varied how the QP changes.

Regards,
Bramhachari Khamari

[Daniele Varsano]

Dear Bramhachari Khamari,
the QP gap is an electronic gap (or transport gap) which is different from an optical gap and it is independent of the pulse.
The QP gap is calculated using the GW approximation and you can read it from the GW output.

Best,
Daniele

[Bramhachari Khamari]

Dear Sir,
Thank you for the reply. I have one confusion in calculating binding energy of the exciton. Binding energy = QP gap- position of the first peak, am I correct. Suppose, the first peak of spectrum shifts towards shorter energy due to variation of the intensity of the pulse, then binding energy should increase. However in the literature reverse is the case.

Regards,
Bramhachari Khamari

[Daniele Varsano]

Dear Bramhachari Khamari,

Binding energy = QP gap- position of the first peak, am I correct

More correctly is QP gap - excitation energy of the first exciton

The exciton can have finite or zero oscillator strength, so it can be bright or dark. When solving the BSE you have access to all the spectrum and the corresponding oscillator strength.

When you excite the system with a laser pulse you can excite different excitons depending on the frequency of the laser.

Best,

Daniele

[Bramhachari Khamari]

Dear Sir,
Thanks a lot for the clarification.

Regards,
Bramhachari Khamari