Mazher, Javed(Prof)Fufa, Fatana2022-04-012023-11-182022-04-012023-11-182013-06http://etd.aau.edu.et/handle/12345678/31057In this piece of research, we have performed self-consistent ab-initio calculations to study the structural and e lectronic properties of BexZnl -xS mixed crystals in the various low and high pressure crystallographic phases of thc alloy. The zinc blend phase and rock salt phase of compositionally variant zinc-bery llium-sulfide have been used for the calc ul ations of' structura l and electronic properties within the local density approximation of density fu nctional theory. The concent rat ion of Be (X) changes f'rom 0.00, 0.41 , and 0.66 to 1.00 in the al loy. Super cells (54 atoms) of the all oys are constructed and fully relaxed. Al l the values of ternary and binary alloy lattice constants, bulk modulus and cnergy band gap are calculated on these relaxed structures. Our results are comparable to the contemporary theoreti cal and experimental observations. Our values for the structural parameters obtained in the LOA approximation are also in good agreement with the experimental values. We have also observed direct band to indirect band gap (r ..... r) ..... (r ..... X) by increasi ng beryl lium concentrations along with some LOA related under estimation s of gap widt hs. For al l the samples of the alloy, high pressure phase tran sitions are found to present and reported in the range of' giga pascal pressures. At the same time, increase of hardening of the al loy is reported due to Be content and the bulk modulus correspondingly increases in the alloy. We have also analyzed the concentration related effects on electronic density of states and bowing parameters.enAb-Initio Calculations of High Pressure Phase TransitionThesis