Yambo Community Forum

Dear Daniele,

I read one of your papers published on PRB (PRB 84, 041401 (2011) Quantum dot states and optical excitations of edge-modulated graphene nanoribbons), form which I learned many. But I still can not plot the figures like Figure 1 and Figure 3 in your paper after many efforts. So, can you please tell me in more detail how to get the Figures:

1) Quasiparticale band structure (Figure 2(b) in you paper). Is it obtained from o.qp? and how if it is?
2) Electron distribudtion of exciton (Figure 3 in you paper).

Thank you very much!

Dear Wei,

1) Quasiparticale band structure (Figure 2(b) in you paper). Is it obtained from o.qp? and how if it is?

Yes, in the o.qp file you have the QP corrections to the DFT energies, just sum them up and plot them versus the k-points value.

2) Electron distribudtion of exciton (Figure 3 in you paper).

Electron distribudtion of exciton, or excitonic wavefunction, you can get it by using the ypp (yambo post processing utility).
You have to solve the BSE equation, by diagonalization and not by recursive methods, activating the flag to save to the eigenvalues,
the flag name is WRbsWF. Next by typing:
ypp -e w
you will have the input file for the excitonic wavefunctions to run with ypp. In the input file you will specify the hope position, the kind
of plot and the file format to be read by visualization softwares (gnuplot, xcrysden, cube format etc...). In the paper you mentioned
Fig.4 is a 2d plot generated with xcrysden.

Hope it helped,

Daniele

Dear Daniele,

Thank you very much for your swift reply, and you patience!
I will let you know when I get the plots.
I have two another questions:

1) What do you mean when you said "In ideal ribbons, the position of the first peak exhibits an oscillating behavior, according to the ... ... (page 041401-2, the last paragraph)"? What is the oscillating behavior?
2) Could you please explain what does "dark exciton" exactly mean?

Excuse me my foolish questions. I am a new guy in this field, and I am now studying the background theory and trying to understand YAMBO.
Many thanks.

Dear Wei Wei,

1) What do you mean when you said "In ideal ribbons, the position of the first peak exhibits an oscillating behavior, according to the ... ... (page 041401-2, the last paragraph)"? What is the oscillating behavior?

Armchair Graphene nanoribbon can be divided in families according their width:
N = 3p − 1, N = 3p, and N = 3p + 1, with p integer, where N indicates the number of dimer lines across the ribbon width.
according to that, increasing the width an oscillatory behaviour of the electronic and optical gap is observed, have a look
to the following papers:

D. Prezzi, D. Varsano, A. Ruini, A. Marini, and E. Molinari, Phys. Rev. B 77, 041404 (2008).
V. Barone, O. Hod, and G. E. Scuseria, Nano Lett. 6, 2748 2006
Y.-W. Son, M. L. Cohen, and S. G. Louie, Phys. Rev. Lett. 97, 216803 2006

2) Could you please explain what does "dark exciton" exactly mean?

A dark exciton is an excitation of the system with zero oscillator strength due to symmetry reason,
and hence not visible in an absorption experiment.

Cheers,

Daniele

Dear Daniele,

Thank you so much!
I will update when I meet new questions.