Richard Jarman - Electronic Structure of Ti(OH)4O2-: A Model for Potassium Titanyl Phosphate

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  Electronic   Structure of Ti(OH)4O2-: A Model for   Potassium Titanyl Phosphate, M. Munowitz, R.H. Jarman and J.F.   Harrison, J. Phys. Chem., 96, 124 (1992).


  Ab initio studies of axially distorted TiO6 octahedra are used to   simulate electronic structure in a system similar to potassium

  titanyl phosphate (KTP), a material noted for its strong   nonlinear optical properties. The C4 model system, Ti(OH)4O22-,

  consists of a planar Ti(OH)4 unit plus O- ions directly above and   below the titanium at the center. Two of the possible electronic

  states are identified: the first, with A symmetry, arising when   the oxygen p(σ)   orbitals along the O-Ti-O axis are only partially

  occupied; the second, a B state, arising when these orbitals are   filled. In the A state, electrons are able to flow from one

  axial oxygen to another through an in-phase combination of   p(σ)   orbitals on the oxygens and the dz2 on the metal. When

  the two oxygens are not equidistant from the titanium, this   mechanism is able to generate a charge asymmetry significantly

  out of proportion to the geometric distortion. In the B state, by   contrast, charge transfer through the σ  system is largely

  precluded since the oxygen p(σ)   orbitals are filled. The equivalent pathway is instead through   the π  system, where the transfer

  from one set of partially occupied oxygen p(π)   orbitals to the other can be mediated by d(π)   orbitals on the titanium. Compared

  to the σ  conduit in the A state, however, the movement of charge between   the two oxygens is less dramatic and less sensitive

  to variations in internuclear distance.

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