Importance of radiation field screening in XPS and XAFS spectra

In this work the importance of radiation field screening is stressed in Keldysh’s Green’s function theory to study X-ray photoelectron spectroscopy (XPS) spectra and X-ray absorption fine structure (XAFS). So far these terms have been supposed to be small, however, we have found that these effects play a crucial role to analyze resonance effects. In particular the importance of these vertex correction is important in the analyses of multiatom resonant photoemission (MARPE) spectra and the resonance effects in XAFS. We also investigate the contribution from polarized part Wp of the screened Coulomb interaction W to the resonance effects. We find that W≈v is quite a good approximation. Off the resonance these radiation field screening diagrams are not important. They have no contribution to loss processes even though they include W> and W<.