First principles computational study of the optical and topological properties of crystalline solids

Abstract

The exploration and study of functional materials represents a critical step in the development of novel devices. Technological requirements, such as dimensionality reduction, enhanced light emission efficiency, and the generation of topological electronic states, can only be fulfilled through appropriate material selection. The objectives of this thesis were to investigate the optical coupling strength at the band edge of two-dimensional materials and to explore the topological signatures of crystalline materials. This investigation was conducted through first-principles computational modelling utilizing the density functional theory (DFT) framework. We performed a high-throughput DFT calculation and comprehensive analysis of the momentum matrix elements between the band edges across a broad spec- trum of nonmagnetic two-dimensional monolayer materials exhibiting direct band gaps. We quantitatively assessed and ranked the optical coupling strength be- tween the valence and conduction band edges. Our findings identified promising materials with optical coupling strengths that are comparable to those found in conventional bulk optoelectronic materials. We proposed a numerical criterion, termed the allowed orbital overlap. This criterion was tested on the ensemble of materials, and the reasons for the outliers behaviour were explored. Additionally, we computed the bimolecular radiative recombination coefficient using DFT for prominent realistic materials.We calculated the spin Berry curvature for two topological insulators. In both instances, we underscore the utility of the spin Berry curvature as a topological marker. To support this framework, we employed negative controls by calculating the spin Berry curvature of two trivial insulators. The orbital angular momen- tum calculated from DFT results was validated against experimental reports on the case of three materials, as well as the spin-projected orbital angular momen- tum for one material case. A strong qualitative agreement was observed between the simulations and the available experimental reports in the majority of cases. This contribution enhances ongoing efforts to bridge theoretical simulations with experimental observations.