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O: Oberflächenphysik

O 40: Oxide und Isolatoren (II)

O 40.7: Vortrag

Freitag, 15. März 2002, 12:45–13:00, H45

An ab initio embedded cluster study of optical excitations below the gap of a NiO(001) surface — •Khompat Satitkovitchai and Wolfgang Hübner — Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, D-06120 Halle, Germany

An embedded cluster approach was applied to study the electronic excitations on the NiO(001) surface. Using the valence Los-Alamos basis set and effective core potentials, quantum chemical calculations of a small cluster (NiO₅)⁸⁻ were done starting at the Hartree-Fock (HF) level of theory. We have begun with HF theory for calculating ground-state properties to provide some insight of electronic structure and excitation. We estimate the band gap and excitation spectra using single excitation Configuration Interaction (CI-Singles) technique. Our HF results yield a charge-transfer (CT) gap of 7.6 eV, which is much higher than the experimental value of bulk NiO (4.3 eV) as expected on the theoretical HF level but yet can be a good starting point to allow for the investigation the low lying d-d intragap multiplet excitations. We then demonstrate the electron correlation effects on the d-d transitions at several levels of ab initio correlated theory (CID, CISD, CCD, CCSD, CCSD(T), QCISD, QCISD(T)). The electron correlation tends to decrease the magnitude of excitation energies. Only at our highest level theoretical methods such as CCSD(T) and QCISD(T), the d-d transition energies (0.53, 1.17, 1.21 and 1.84 eV) are found to compare well with the experimental data.