Interpreting TDHF results

[guyohad]

Dear VASP developers,

I have two question regarding the interpretation of the output obtained from a TDHF calculation in the vasprun.xml file.

• In the internally interpreted dielectric tensor, i.e. the one represented by <dielectricfunction><imag> and <dielectricfunction><real>, what is the magnitude of the broadening? I am aware that the CSHIFT flag is the way to control the broadening, but according to VASP wiki it does not seem to be the value of the broadening itself.

• In the <opticaltransitions> array, it is obvious that the numbers in the left column represent energy in units of eV. My question here is what is the right column? It must represent some kind of intensities, but what is the exact quantity that they represent and in what units?

I appreciate any help,
Sincerely,
Guy

[alexey.tal]

Dear Guy,

In the internally interpreted dielectric tensor, i.e. the one represented by <dielectricfunction><imag> and <dielectricfunction><real>, what is the magnitude of the broadening? I am aware that the CSHIFT flag is the way to control the broadening, but according to VASP wiki it does not seem to be the value of the broadening itself.

I am not sure I fully understand your question. What page on the wiki are you referring to? As you correctly said CSHIFT is the tag that sets the Lorentzian broadening (complex shift) in the dielectric function.

In the <opticaltransitions> array, it is obvious that the numbers in the left column represent energy in units of eV. My question here is what is the right column? It must represent some kind of intensities, but what is the exact quantity that they represent and in what units?

The first column in <opticaltransitions> is the energy of the transition in eV and the second column is the corresponding oscillator strength. Since it is the portability of the transition, it should be unitless.

[guyohad]

Dear Alexey,

Thank you for your answer.

For the first part, I will simplify my question: when setting CSHIFT=0.12, does that mean that the broadening is 0.12 eV?
For the second part, your answer helps a lot, but is it possible to ask for the exact expression that is used to calculate this?

Thank you,
Guy

[alexey.tal]

Sorry for the late reply.

For the first part, I will simplify my question: when setting CSHIFT=0.12, does that mean that the broadening is 0.12 eV?

Yes.

For the second part, your answer helps a lot, but is it possible to ask for the exact expression that is used to calculate this?

The optical transitions written in vasprun.xml are calculated this way: