Many-body calculations of the valence photoemission spectra of NiCO, PdCO and PtCO

Abstract

The valence photoemission spectra of NiCO, PdCO and PtCO are calculated by the ab initio Green's function method using an extended basis set. The present ab initio many-body approach gives a reasonably good description of the valence photoemission spectra of CO adsorbed on Ni, Pd and Pt metal surfaces. A detailed analysis of the spectral features of the valence photoemission spectra of NiCO, PdCO and PtCO is made. For the 1π level of NiCO and PtCO the quasi-particle picture (QPP) breaks down, however, for PdCO the QPP is still valid. For the 4σ and 5σ levels of NiCO, the lowest energy state is the main line single-hole (1h) state not the CT (charge transfer) 2h 1p (two hole one particle) shakedown state. However, for PdCO and PtCO, the σ (π) to π∗ metal-ligand CT 2h 1p shakedown state of a non-negligible intensity becomes the lowest energy state. The main line state is still the 1h state and the QPP ios valid. For the PdCO and PtCo where the π bonding is considered to be weaker than for NiCo, the CT screening from the σ metal orbital becomes substantial because of a weaker π bonding.