First-principles calculational methods for surface-vacancy formation energies, heats of segregation, and surface core-level shifts.

Abstract

The matrix Green's-function version of the self-consistent scattering theory of surface-point-defect energetics is extended to the cases of vacancy formation, substitutional adsorption, and surface core-level shifts. Vacancies are treated by zeroing Hamiltonian and overlap matrix elements involving orbitals of atoms being removed and crystal orbitals or the crystal potential. Substitutional adsorption is treated as ordinary adsorption in a vacancy, a treatment which permits use of an arbitrary number of substitutional-atom basis orbitals. Surface core-level shifts, including final-state relaxation effects, are obtained from substitutional adsorption calculations via the Born-Haber-cycle argument of Rosengren and Johansson. In a first comparison with experiment, the surface core-level shift for Al(001) is predicted to be -97 meV, modeling this system as a five-layer film, while different experimental groups report values ranging from 0 to -120 meV, respectively, for the Al(2p) level. Earlier calculations, which neglected final-state relaxation, predict a shift of -94 meV for the Al(1s) and about -120 meV for the Al(2s) and Al(2p) core levels. Comparison with the present result indicates that relaxation effects are small in the Al(001) surface core-level shift.