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 calcu lated within a cluster model. The model takes into account intra-atomi c d-d and d-core electron correlation in the transition metal adatom a s well as hybridization between transition metal d and graphite pi orb itals. The spectra and the magnetic state of the adatom are studied as a function of adatom-surface distance h. When h is increased, the tra nsition metal atom undergoes a low-high spin transition, where the tot al spin switches from 0 or 1/2 to the Hund's rule value. This transiti on can be explained by the competition between the d-d exchange splitt ing and an effective crystal field splitting. In the low spin regime t he spectra show essentially one charge transfer satellite, which is qu ite large for the Fe adatom, In the high spin regime, exchange and cha rge transfer satellites are mixed leading essentially to a three peak structure. Only at adatom-surface distances much higher than the equil ibrium value do the spectra show the simple atomic-like exchange split ting. (C) 1998 Elsevier Science B.V. All rights reserved.