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

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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 5σ and 4σ 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 5σ and 4σ ionization, the 2h-1p CT shakedown state becomes more stable than the 1h state because of a weaker π donation in the ground state in PtCO and PdCO in comparison to NiCO. For the 1π 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.