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Investigations of Point Defects in KH2PO4 Crystals Using Ab Initio Quantum Methods


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Potassium dihydrogen phosphate crystals can be grown to large sizes and are used for many important devices for high powered lasers. The nonlinear optical material has a wide intrinsic transparency range. Intrinsic point defects are responsible for several short-lived absorption bands in the visible and ultraviolet regions that affect operations. The primary intrinsic defects have been experimentally detected in KDP using electron paramagnetic resonance (EPR) experiments. The defect models established include (i) self-trapped holes, (ii) oxygen vacancies, and (iii) hydrogen vacancies. In this research, the quantum chemistry Gaussian software program was successfully used to establish the atomic displacements forming the potential well to "self-trap" the hole in an otherwise perfect region of the crystal. The Gaussian results provide isotropic and anisotropic hyperfine predictions for the self-trapped hole and simulated EPR spectra are in excellent agreement with prior experimental work. This research further develops the understanding of the overlap of spin density on neighboring ions in KDP and the resulting nuclear hyperfine values which can be compared to EPR data. The best approach determined by the modeling of self-trapped holes is also applied to the cation and anion vacancy problems. Work was performed on the DOD's High Performance Computer.



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