Krizek, EAR; (2015) Computational Study of Radiation-Induced Defects in Topaz. Doctoral thesis , UCL (University College London).

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Abstract

This purely theoretical investigation considered the irradiation induced and other intrinsic defects that may form colour centres in topaz. Topaz is an aluminium ouro/hydroxy-silicate and undergoes a colourless to blue optical transformation during irradiative treatment. The depth of hue and quality of the colour is dependent on the type of radiation used, whether thermal annealing was involved, and the origin of the samples. Since the colour centres for any of these processes are not well understood for topaz, a detailed investigation into all likely defects cited in the literature was performed. Ground state electronic structure calculations, using full electron basis sets and hybrid functionals, were performed using the CRYSTAL and CP2K codes, to gain the relative stabilities and structural properties of optimised open shell defect models; as well as the density of states, localised spin densities, and certain EPR parameters. The molecule dynamics time-dependent density functional theory (MD TD-DFT) scheme within the CP2K code was used to generate calculated UV-Vis spectra to compare with experimental data supplied by literature.

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