BSE+GW (hexagonal boron nitride)

[davood]

Hi
I want to get optical spectra for pure h-BN with GW+BSE.(Phys Rev B.83.144115 "Coupling of excitons and defect states in boron-nitride nanostructures").
So, I did the following steps:
1-scf (with QE)
2-nscf (with QE)
3-./yambo -g n -p p
4-./yambo -b
5-./yambo -o b -y h
files also attached.
What changes do I need?(in input files)


Best Regards
Davoud Vahedi,

Dept. of Physics,
Faculty of Science,
Ferdowsi University of Mashhad ,
Mashhad ,
Iran .

[claudio]

Dear Davoud Vahedi

your inputs seem correct and also your spectra.
Please check the distance between the BN sheets, in the PRB it was 20 a.u., and look at the notes at the end of the paper
for the parameters used in the calculations.
Some other advice:
*) you can run BSE directly with the dielectric constant calculated in the GW calculation doing
yambo -o b -y h -p p
if you want also the excitonic wavefunctions you have to diagonalize the BSE hamiltonian with
yambo -o b -y d -p p
(see here http://www.yambo-code.org/doc/docs/doc_BSS.php#diago)

*) GW calculations take a lot of memory for large cells, try to run yambo -M to ditribute part of the memory among
the different CPU.

*) increase the number of k-point to check if results are converged

*) use a cutoff for the Coulomb interaction along the Z direction in such way to reduce the interaction among the different sheets,
just add -c to generate the inputs, for example for the GW yambo -g n -p p -c
(see here http://www.yambo-code.org/doc/inputs/input_rimcut.php)
and then set

RandQpts= 3000000 # [RIM] Number of random q-points in the BZ
RandGvec= 1 RL # [RIM] Coulomb interaction RS components
........
CUTGeo= "box z" # [CUT] Coulomb Cutoff geometry: box/cylinder/sphere
% CUTBox
0.00000 | 0.00000 | 14.00000 | # [CUT] [au] Box sides
%

the cutoff in z depends from the distance of the sheets, it should less than half-distance.

Best Regards
Claudio Attaccalite


Best Regards
Claudio Attaccalite