questions in o.exc_weights_at

[xixi]

Dear Developers;

I can not totally understand the file o.exc_weights generated by ypp -e a


# Band_V Band_C K ibz Symm. Weight Energy
#
45.00 46.00 27.00 1.000 0.2703E-1 0.5695E-1
45.00 46.00 27.00 2.000 0.2703E-1 0.5695E-1
45.00 46.00 26.00 7.000 0.2288E-1 0.5771E-1
45.00 46.00 26.00 6.000 0.2288E-1 0.5771E-1
45.00 46.00 26.00 5.000 0.2288E-1 0.5771E-1






could you tell me something about the meaning of "Weight " and "
Energy" in the output


Thanks!

[Daniele Varsano]

Dear Xi Zhu,
let me remind you first to fill your signature with the affiliation in your account.

When solving the Bethe Salpeter equation you are in the transition basis. Your basis is
formed by the KS electron-hole pair (valence/conduction wave functions). Thus, the
eigenvector corresponding to the chosen eigenvalue (excitation energies) are linear
combinations of such transitions. The weights are indeed the square coefficients of the
KS transitions participating in the excitations you have chosen to analyze.
If you have a look to the documentation,
they are the A^{lambda}_{cv} (squared) coming from the diagonalization of the excitonic matrix.
With this information you can get insight on the character of the excitation.

The energy, is simply the KS energy differences of the transition corresponding to the
valence/conduction indicated in the first columns (c,v,k,symm) which is participating in the
excitation with the indicated weight.

Cheers,

Daniele