Publication Details (including relevant citation information):
Theoretical Study of the Nonlinear Optical Properties of KTiOPO4: Effects of T-O-Ti Bond Angles and Oxygen Electronegativity, M. Munowitz, R.H. Jarman and J.F. Harrison, Chem. Mater., 5, 1257 (1993).
Second harmonic generation in the model system [TiO5--TiO6--TiO5]20- is studied using a
perturbative sum-over-states formalism together with extended Huckel wave functions. The
nonlinear response of the central TiO6 group, a distorted octahedron with its fourfold axis
defined by the atoms O1--Ti--O2, improves both with increasing Ti--O--Ti angle and with
decreasing electronegativity of the chain oxygens. A small shift of charge toward the distant
oxygen, O1, takes place as the Ti--O--Ti angle is increased, thereby enlarging the electronic third
moment and with it the local hyperpolarizability. Reducing the electronegativity of the oxygens,
by contrast, brings about a near-resonant enhancement of the hyperpolarizability, which occurs
as energies of the highest occupied molecular orbitals are raised. These results are placed in
the context of recent experimental measurements involving compounds isomorphic to KTiOPO4.
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