Simple Model for Dynamic Relaxation

As already mentioned before, if one could localize a core hole on a given nucleus it would oscillate with a hopping frequency determined by the level splitting Wa, and the n-charge would have a relax in the presence of a moving hole, i.e. dynamic relaxation. However, for a deep core hole the hopping frequency would be practically zero and we would then have static relaxation (cf. Sect. 3). We shall now discuss these two cases in some detail. 

Quasi-Particle Properties of Hole Levels in Molecules 

The static monopole relaxation diagram clearly describes the response to a delocalized core hole while the dynamic relaxation (fluctuation) process describes the response to the dipole moment of the hole. Together, the two diagrams (Figs. 38c,e) describe the response of the system to a hole localized to an atomic core orbital on either nucleus41, and individually they represent a multipole expansion of the hole. 

When the hopping frequency of the a-hole is equal to the resonance frequency of the jr-bond there are two equally important normal modes of the total system o-hole and 7r-bond, one where the hole and screening charge oscillate together in phase between the 

2 Self-Energy and Spectral Function for a Realistic Model of Multiple-Bonded Molecules 

---