identifying transitions from BSE/TDHF output

[awang95]

Hi,

I have the optical transitions from the vasprun.xml file for a BSE/TDHF calculation. However, in addition to the energies of each transition I'm interested in knowing the bands/orbitals involved in that specific transition (i.e. from which band to which band does the transition correspond to). I can't seem to find the corresponding information in the output files...could you please help me with this? Alternatively, if there are suggestions for any post-processing software that can do this that would be awesome as well

thanks!

[alexey.tal]

Hi awang95,

You can find this information, i.e. the contribution of the individual transitions into the excitonic state, in the BSEFATBAND file.

[awang95]

thanks!

should the highlighted part of this picture from the wiki be NB_e?

[awang95]

sorry I would like to clarify another thing

from the BSEFATBAND output it seems that the values correspond to the below as noted (it only makes sense if I interpret it this way), which is different from the order posted on the wiki - can I confirm whether if the below would be correct? thanks

[alexey.tal]

It's a typo, thanks for pointing that out. Actually, these are the valence and conduction band energies and numbers, so I changed the notation on the wiki accordingly. Does that answer your question?

[awang95]

yes thanks!

[awang95]

sorry just like to follow up on this as I'm now interested in the eigenvectors: I'm not quite sure what it means when the wiki says "X_BSE" corresponds to the "component of the eigenvector" - is it the component in the x-direction only or something else? I think I'm not really sure which eigenvector and what component of it the "X_BSE" is referring to here. Also, what physical information can we extract from Abs(X_BSE) and Re(X_BSE)+i*(X_BSE)? sorry if this is too obvious or stupid - I'm still quite new to this and have been quite confused for a while

thanks!

[alexey.tal]

The BSEFATBAND file stores the eigenvectors of the BSE Hamiltonian found when we diagonalize the Hamiltonian. X_BSE are the components of the these eigenvectors which are essentially the coupling coefficients or contributions of individual transitions between valence and conduction bands. Using this information you can make a fatband plot as described on the wiki Plot BSE fatbands. Such a plot can give you an idea of what transitions contribute the most to an excitonic state and how localized this state is.

[awang95]

ok thanks so much!