Multiscale ab initio approaches to materials physics

Abstract

This work presents new ab initio approaches to materials physics. We first introduce the multiscale approach to determination of thermal properties and changes in free energy. With this approach one can perform thermal averaging of ensembles of states with ab initio methods, thus enabling ab initio calculations of free energy changes. We use this method to perform an ab initio calculation of the free energy of reconstruction in the 300 reconstruction of silicon. In the next chapters we introduce a completely new approach to electronic structure calculations, using a new, real-space bais set (wavelets) which enables all-electron calculations of complex systems. By eliminating the need for pseudopotentials for decsribing the core, one can for the first time access the true density functional energy of a system through systematic convergence. In the final chapter we combine this method with the generalized gradient approximation to perform calculations on high-pressure phases of boron.