# Regensburg 2004 – wissenschaftliches Programm

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# O: Oberflächenphysik

## O 44: Elektronische Struktur (Experiment und Theorie) III

### O 44.7: Vortrag

### Freitag, 12. März 2004, 12:45–13:00, H38

**Second Harmonic Generation on NiO** — •Georgios Lefkidis, Khompat Satitkovitchai, and Wolfgang Hübner — TU Kaiserslautern, PO Box 3409, D-67653, Germany

The second
order susceptibility tensors, which are important for Optical
Second Harmonic Generation (SHG) are studied for NiO starting from
*ab-initio *calculations. To represent the (001) surface of
the rocksalt NiO lattice we embed a NiO_{5}^{−8} cluster in a
charge point field which accounts for the Madelung potential due
to the neighboring ions. Similarly, an embedded NiO_{6}^{−10}
cluster is used to represent the bulk. The quantum chemical
calculation is performed at various levels, where the effect of
the basis set is studied, and the energy correction due to
electron correlations. A Complete Active Space Configuration
Interaction is performed, while the excited states are studied
with Single Excitation Configuration Interaction (CIS) with energy
contribution from double and triple excitations. The electric and
magnetic dipole transitions are used to calculate the
χ_{eee}^{(2ω)} and χ_{mee}^{(2ω)} tensors.

While inversion symmetry of the bcc lattice leads to zero tensor
elements for the bulk, the breaking of the symmetry on the surface
gives non-zero elements within the electric-dipole approximation.
On the other hand some χ_{mee}^{(2ω)} elements exist for
both bulk and surface. The effect of spin-orbit coupling on both
tensors is discussed.