Yambo Community Forum

Dear Developers,

Would you explain me about the meaning of the symmetry numbers (symm. = 1 or symm. = 3) in the
o.exc_weights_at file??

Thank you in advance

Dear Samaneh,

the symmetry index in the o.exc_weights_at file is the number of symmetry as indicated in any report file, where the symmetries found are numbered and the symmetry matrix is explicitely reported. Number 1 is usually the identity.

Best,

Daniele

Dear Daniele,
Thank you for your quick reply.
But actually I can not understand that why I have two values of weights for one point (like gamma)
because I have a weight of 0.622699 for the gamma point as it is in the file :
# Electron-Hole pairs that contributes to Excitonic State 8 more than 5%
#
# K-point [iku] Weight
# 0.000000 0.000000 0.000000 0.622699
# 0.000000 0.000000 0.166667 0.248437
# 0.000000 0.000000 0.333333 1.000000
# 0.000000 0.000000 -0.500000 0.504632
#
but here we see 0.46083 value for it??
# Band_V Band_C K ibz Symm. Weight Energy
#
47.00000 49.00000 1.00000 1.00000 0.46083 3.90337
48.00000 49.00000 1.00000 1.00000 0.46081 3.90341

can you explain the relation between the two different weight values of the same K point (e.g. for the first K=gamma)??

Dear Samaneh,
careful, they have a totally different meaning.

In the first file is the weight of the K point in the sampling of the BZ and it has nothing to do with the exciton, it depends on the symmetry of the BZ.
The seconds are the weights of the single transitions forming the exciton.

Best,

Daniele

Thanks a lot.
But, How can we understand which transition is dipole allowed or not?

In first instance, looking at the spectrum file you can see peaks having reasonable intensity at the excitation energy.
In the output file o.exc_E_sorted, or o.exc_I_sorted, the intensity of the excitation is also reported

Best,
Daniele