Regensburg 2004 – scientific programme

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O: Oberflächenphysik

O 34: Oxide und Isolatoren

O 34.2: Talk

Thursday, March 11, 2004, 11:30–11:45, H45

Ab initio embedded cluster study of optical second harmonic generation below the gap of the NiO(001) surface — •Khompat Satitkovitchai and Wolfgang Hübner — FB Physik, Technische Universität Kaiserslautern, Erwin-Schrödinger-Straße, D-67663 Kaiserslautern

An embedded cluster approach is applied to study the electronic excitations on the NiO(001) surface. Using a quantum chemistry calculation, a small (NiO₅)⁸⁻ cluster is embedded in a set of point charges to model the NiO(001) surface. Starting on the unrestricted Hartree-Fock (UHF) level of theory we calculate ground-state properties to provide some insight of electronic structure and excitation. We estimate the excitation energies using the single excitation configuration interaction (CIS) technique. We then demonstrate the electron correlation effects on the d–d transitions at several levels of ab initio correlated theory (CID, CISD, QCISD and QCISD(T)). The electron correlation tends to decrease the magnitude of d–electron excitation energies. Using the many-body wave-functions and energies resulting from QCISD(T) calculation we compute the second harmonic generation (SHG) tensor for the NiO(001) surface. From that, the intensity of the non-linear optical response at different polarizations is obtained. This quantity can be directly measured in experiment, and we suggest possible conditions in order to detect it.