First-principles study of structural, vibrational, and dielectric properties of crystalline and amorphous oxides

This thesis embraces essentially the study of two kinds of insulators, highly-compressed solid molecular hydrogen and metal oxide dielectrics (crystalline and amorphous).; For compressed solid hydrogen (Chap. 3), we investigate whether the essential physics of Wannier functions can be captured by a tight-binding (TB) approach (sp3) applied on certain prototype structures of solid molecular hydrogen, based upon the facts that the TB approximation provides a simple and inexpensive method for computing electronic structure effects, and its output is easily interpreted in terms of a local, real space picture. Our intention is to study the dielectric properties of H₂ from this local point of view, and it is demonstrated that the TB model we used provides useful insights into the nature of Wannier functions and their contribution to the electronic polarization.; The following chapters, associated with oxide dielectrics, are primarily motivated by the substantial ongoing efforts directed toward finding a replacement for SiO₂ as the gate dielectrics in complementary metal-oxide-semiconductor (CMOS) devices. ZrO₂, HfO₂ and their structure-modified derivatives show great promise for this purpose. We perform a first-principles study of the structural and vibrational properties of the three low-pressure (cubic, tetragonal, and especially monoclinic) phases of ZrO₂, with special attention to the computation of zone-center phonon modes and the related dielectric properties. The corresponding work is extended to HfO ₂ using similar techniques. In this latter work, we provide the first thorough theoretical study of the structural, vibrational and lattice dielectric properties of the low-pressure HfO₂ phases.; Realistic models of amorphous ZrO₂ are then realized using ab-initio quantum-mechanical molecular dynamics in a “melt-and-quench” fashion, with ultrasoft pseudopotentials and a plane-wave basis set in the local-density approximation. The generated amorphous ZrO₂ structures are then analyzed in order to comprehend their structural properties and local bonding arrangements, and can be used to investigate the vibrational properties and dielectric responses of those disordered ZrO₂ systems from first-principles.