Vibrational Properties Of Solids PDF Download

This dissertation describes first-principles quantum mechanical investigations of several realistic solid-state systems. The main goal of this research has been to understand and predict the electronic, vibrational, and structural properties of materials under pressure. Microscopic information on these properties is obtained within local density functional theory using ab initio pseudopotentials. This work focuses on three categories of materials: (1) Part I deals with the high-pressure behavior of elemental systems from group IV of the Periodic Table. The pressure-dependences of Raman-active phonon modes of high-pressure, metallic phases of silicon, germanium, and tin are studied within the frozen-phonon approximation. In addition, the structural properties of a recently discovered orthorhombic phase of silicon are calculated. The aim of these two investigations is to understand and explain recent experimental results. A third investigation predicts the existence of an orthorhombic, high-pressure phase of germanium. (2) Part II focuses on group V of the Periodic Table. The electronic and vibrational properties of elemental arsenic are studied with the aim of understanding the measured pressure-dependences of the superconducting transition temperature and the normal-state resistance. In addition, several candidate atomic phases of solid nitrogen are studied to determine their structural-stability and electronic properties. (3) Finally, Part III considers the effect of varying the stoichiometry in compound systems. In particular, model calculations are performed to explore the Ga-As system with the goal of motivating experimental studies. The electronic properties of several model Ga-As systems with varying stoichiometry are studied.