Many-body calculation of the valence photoemission spectra of PdCO and PtCO.

Abstract

The valence photoemission spectra of PdCO and PtCO are calculated by the ab initio third-order algebraic-diagrammatic-construction Green's-function method using an extended basis set. The overall agreement with the experimental spectra of CO on a Pd(100) and a Pt(111) metal surface is good. A comparison of the spectral features among NiCO, PdCO, and PtCO is made. For the 5\ensuremath{\sigma} and 4\ensuremath{\sigma} levels of PdCO and PtCO, the quasiparticle picture (QPP) is valid as in the case of NiCO. However, in PtCO and PdCO, the lowest-energy state is not the main-line 1h (one-hole) state but the 2h-1p (two-hole, one-particle) metal-ligand charge-transfer (CT) shakedown state which has a substantial intensity (0.02--0.29 for PdCO and 0.01--0.13 for PtCO). This state is induced by the hole-hopping dynamical relaxation. The second-lowest-energy state of a large intensity (0.51--0.76 for PdCO and 0.62--0.74 for PtCO) is the main-line 1h state. For the 5\ensuremath{\sigma} and 4\ensuremath{\sigma} ionization, the 2h-1p CT shakedown state becomes more stable than the 1h state because of a weaker \ensuremath{\pi} donation in the ground state in PtCO and PdCO in comparison to NiCO. For the 1\ensuremath{\pi} excitation, the QPP is still valid for PdCO in contrast to NiCO for which the QPP breaks down due to the metal-ligand CT static relaxation. The lowest-energy main-line state of a large intensity (0.62) is still the 1h state. For PtCO this main line loses a large intensity to the first satellite and the intensity of the two lines becomes nearly comparable.