Calculation of 3s photoemission spectra of 3d transition metal atoms adsorbed on graphite

The 3s photoemission spectra of V and Fe adatoms on graphite are calculated within a cluster model. The model takes into account intra-atomic d-d and d-core electron correlation in the transition metal adatom as well as hybridization between transition metal d and graphite pi orbitals. The spectra and the magnetic state of the adatom are studied as a function of adatom-surface distance h. When h is increased, the transition metal atom undergoes a low-high spin transition, where the total spin switches from 0 or 1/2 to the Hund's rule value. This transition can be explained by the competition between the d-d exchange splitting and an effective crystal field splitting. In the low spin regime the spectra show essentially one charge transfer satellite, which is quite large for the Fe adatom, In the high spin regime, exchange and charge transfer satellites are mixed leading essentially to a three peak structure. Only at adatom-surface distances much higher than the equilibrium value do the spectra show the simple atomic-like exchange splitting. (C) 1998 Elsevier Science B.V. All rights reserved.