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).

  Abstract:

  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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