Modeling Nanomaterials with Efficient and Accurate Electronic Structure Methods

Abstract

Electronic structure methods are one of the most powerful tools in the computational toolbox to provide an atomistic understanding of molecules and materials. Among all electronic structure methods, Density functional theory (DFT) has become the standard choice for electronic structure calculations on molecules, clusters, surfaces, and solids, with thousands of papers published and new, improved, and more accurate functionals proposed almost every year. DFT methods have also gained great success in understanding the structural, thermodynamic, and electronic properties of nanomaterials like quantum dots and perovskite solar cells. However, with a growing demands for a deeper understanding of those nanomaterials, DFT has reached a bottleneck. Either the material system we are looking into is too complicated to be handled by DFT under current computational resources, or the physics we are targeting is beyond the capability of DFT. Therefore, more accurate and efficient methods need to be developed to better study nanomaterials. This dissertation covers both success stories of nanomaterials modeling by DFT, and efforts of developing new electronic structure methods for nanomaterials. After a brief introduction to the preliminary theory concepts in Chapter 1, Chapter 2 focuses on using DFT to rationalize experimental findings and predict the chemical and physical properties of the lead halide perovskites. Chapter 3 demonstrates the effort of pursuing the tractability of electronic structure methods to handle even larger chemical systems with no periodicity. Chapter 4 focuses on including relativistic effects in electronic structure methods with the goal of accurate modeling of the wave functions of nanomaterials. Chapter 5 focuses on modeling external field and environmental effects. Though the benchmark and examples to the methods detailed in Chapter 4 and 5 are not real nanomaterial systems, the implementations are general and fully compatible to study the nanomaterial systems like metal or semiconductor clusters.