Introduction

The quantitative description of the structural, electronic, and optical properties of metals, semiconductors, and insulators is one of the long-standing challenges of condensed matter physics. Theoretical methods in combination with computational tools currently provide a reliable understanding of the properties of bulk materials. More complicated systems such as extended defects, grain boundaries, dislocations, etc. are currently under investigation.

At Ohio State, we use high-performance computing on massively parallel architectures to describe the properties of semiconductors, insulators, and metals. Examples of this effort can be found under the links given above.

Structure is generally determined by total energy calculations or by molecular dynamics calculations. Often, we use a hierarchical approach: We start investigating a system with classical potentials, which describe the interaction between atoms by pair potentials, to get a rough idea of the fundamental processes in and properties of a system. Then we refine our understanding by using tight-binding. Finally, detailed questions regarding structure and stability are answered by first-principles calculations based on density functional theory in the local density or generalized gradient approximations.

The electronic structure is determined by quasiparticle calculations in the so-called GW approximation. These calculations allow an accurate determination of the electronic structure of materials (to within 0.1-0.5 eV). Input for quasiparticle calculations comes either from LDA or exact-exchange-plus-LDA-correlation density functional calculations (see also Density Functional Theory). We have developed parallel codes both for a real-space and a reciprocal-space GWA calculation.

Last but not least, we determine the linear and nonlinear optical properties of materials from first-principles. Here, we include - in contrast to most other groups - local field effects in the calculation. Local field effects describe screening because of an inhomogeneous density distribution in a solid and are not negligible. They amount to about 10-15% for the dielectric constant, 10-30% for the coefficient of second-harmonic generation, and about 100% for the coefficient of optical activity.

Topics Covered

Structural Properties

Diffusion in Liquid Germanium

Defects in Silicon

Electronic Properties

Review of Quasiparticle Calculations

Valence band off-set in GaN/AlN systems

Optical Properties

General

Electro-Optic Modulation in SiGe

Exotic Materials

Skutterudites

Superconductivity