First-Principles Calculations of the E′1 Center in Quartz: Structural Models, 29Si Hyperfine Parameters and Association with Al Impurity
The oxygen-vacancy-related E′ 1 center in quartz is a prototype defect in SiO2-based materials and has been intensively studied by experimentalists and theoreticians for more than 50 years, but questions remain about its structural model and formation mechanism. We have conducted first-principles calculations for the E′ 1 center in quartz by using the supercell approach with Gaussian-type all-electron basis sets and hybrid functionals as implemented in the ab initio code CRYSTAL06. Our calculations, featuring both the traditional single-oxygen-vacancy model and a new tri-vacancy model with one silicon and two oxygen vacancies, have improved the reproduction of the experimental 29Si hyperfine parameters than previous theoretical studies. In particular, our calculated hyperfine coupling constants for the strong and two weak 29Si hyperfine structures from the new tri-vacancy model are all within 5% of the experimental values, and the calculated directions of the principal hyperfine axes are in agreement with the experimental results as well. Moreover, the tri-vacancy model can account for the common association of the E′ 1 center with the [AlO4]0 center and superoxide O2 − radicals in quartz.
KeywordsElectron Paramagnetic Resonance Oxygen Vacancy Hyperfine Coupling Constant Natural Quartz Unpaired Spin
We thank Prof. Jens Götze for invitation to the special session on quartz at BHT2011, Drs. Robert Möckel and Michael Plötze for manuscript review and handling, and Natural Science and Engineering Research Council (NSERC) of Canada for financial support. All calculations in this research have been enabled by the use of Westgrid computing resources, which are funded in part by the Canadian Foundation for Innovation, Alberta Innovation and Science, BC Advanced Education, and the participating research institutions. Westgrid equipment is provided by IBM, Hewlett Packard and SGI.
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