Absolute quasiparticle energies for finite systems

[twospaces]

Dear board members,

I am a new Yambo user - please forgive my naive questions:
I try to compute ionization potentials and electron affinities for some molecules and managed to get a quite reasonable QP gap with Yambo. Usually, absolute energies with respect to the vaccuum level are not straightforwardly obtained in periodic calculations. Is there a way to relate the QP energy of the HOMO given by YAMBO to an IP? Possibly the offset needs to be evaluated already at the DFT level (I am using pwscf), e.g. by evaluating the potential far away from the molecule or on the cell boundary. Has anybody experience with this kind of correction?

Any help is highly appreciated!
Best Thomas

[Daniele Varsano]

Dear Thomas,
I have not experience on evaluation of absolute value of IP and EA,
anyway, if the QP correction has been converged with respect the supercell
volume, I presume that the way you suggest should be correct, as the vacuum level
should be the one coming from the DFT calculation. But again, I have no direct experience
on that, and someone else could answer to your question with more knowledge.

Cheers,

Daniele

[claudio]

Dear Thomas

I think you should use one of the "assume_isolated" flag in PWSCF in such a way to get an
estimate of the vacuum level to align the eigenvalues. Then you can correct them with GW.
Check the "cluter_example". But I never did it.

Claudio

[twospaces]

I will try that. Thanks a lot!

- Best Thomas