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Session C21 - Electronic Structure Theory: Semiconductors, Insulators, and Their Defects.
MIXED session, Monday afternoon, March 18
Room 263, America's Center
We present first-principles, embedded-cluster calculations on the impurity system CaF_2:Mn^2+. The system is represented in the local spin density approximation by a cluster of 51 atoms embedded in an infinite fluorite array of point charges. The Madelung potential is represented by a technique developed by Tosi. The electronic structure code is one developed by Pederson and Jackson featuring a variational method for accurate numerical integration. We have exploited that feature in modifying the code to allow for embedding. Our use of a large cluster and extensive basis functions ensures a good representation of the local defect region and the host features (band gap, valence band) which are important in determining the electronic structure. The embedding technique ensures proper placement of defect levels relative to host band states. We find that the ground state is a high-spin ^6A_1g state in agreement with other calculations. Our value for the spin density at the Mn site is in good agreement with experiment. We also present some of the optical features of this center related to electron transfer bands and their positions relative to the expected interconfigurational transitions (3d->4s, 4p).
