9-13 July 2012
Africa/Johannesburg timezone
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Theoretical calculation of positron states and annihilation rates in BaF2

Presented by Mr. Thulani JILI on 10 Jul 2012 from 17:30 to 19:30
Type: Poster Presentation
Session: Poster Session
Track: Track A - Division for Condensed Matter Physics and Materials

Abstract

Theoretical calculations for electronic structure are a valuable technique in the analysis of positron annihilation experiments. Theoretical calculations predict measured quantities such as annihilation rates and momentum distributions of annihilating electron-positron pair corresponding to vacancy-type defects trapping free positrons. Core electron annihilations are explained using free atom wavefunctions. The enhancement factor, g, was used in the Generalized Gradient Approximation (GGA) to influence both the fluorine and barium electronic annihilation rates. In the GGA, the annihilation rate in fluorine and barium ranges from 0.112 x 10<sup>9</sup> s<sup>-1</sup> to 1.580 x 10<sup>9</sup> s<sup>-1</sup> (1s – 2p) and from 0.011 x 10<sup>9</sup> s<sup>-1</sup> to 2.017 x 10<sup>9</sup> s<sup>-1</sup> (1s – 6s) respectively. Positron lifetimes of delocalized and localized positron in BaF<sub>2</sub> was calculated in the Two-component Density Functional Theory (TCDFT) and found to be 189.60 ps and 203.67 ps respectively. This is a confirmation of vacancy type defect at ambient temperature.

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