UC Berkeley

Electronic structure theory enables fundamental understanding of material properties. Using first-principles based methods, several different classes of complex materials are studied including perovskite oxide heterostructures, halide perovskites, alkali metals under pressure, and high-throughput screening of multiferroic materials.

• In Chapter 2 we discuss the basis of electronic structure methods used in this thesis and introduce the calculation of topological properties from first-principles.

• In Chapter 3 the properties of lithium, an ostensibly simple metal, under pressure are introduced and our explorations into the emergence of nontrivial topological features at high pressures are shown.

• Halide perovskites have emerged as a promising material class for solar energy con- version due to their optoelectronic properties. We explore three different halide per- ovskite materials and, in collaboration with experiment, develop an understanding of how their properties change through chemical substitutions and structural manipula- tions. This includes the optoelectronic properties of Sn–alloyed Cs2AgBiBr6 (Chapter 4) and Cs8Au4XCl23 (X = In; Bi) (Chapter 6); and the increase in conductivity of (EA)2CuBr4 through pressure (Chapter 5).

• Similarly, perovskite oxides are a highly tunable class of materials which display a wide range of interesting phenomena. Here we exploit the fact that experimentalists can control the synthesis of perovskite oxide heterostructures at the precision of single atomic layers. Given this level of control, we use first-principles calculations to de- sign monolayers and bilayers that would tune the work function of bulk SrRuO3 for thermionic applications in Chapter 7

• In Chapter 8, we discuss our work developing a high throughput workflow based on symmetry and first-principles calculations to screen tens of thousands of materials for candidates which are both magnetic and ferroelectric.

• Finally, Chapter 9 presents an overview of the work.