First-Principles Studies of Energy-Related Materials

The energy crisis is one of the biggest issues our modern society has witnessed, and a green energy revolution must be made to maintain the sustainable development of society. This thesis contains several applications of the first-principles electronic structure theory used in the study of energy-related materials. First, we give a brief review of the basic first-principles electronic structure theory. Next, we study the water splitting reaction on the anatase TiO2 (001) surface. We find a slightly modified surface of the TiO2 layer has significantly improved ability to split water. We show by explicit calculation of the water splitting reaction that the energy barrier that exists on a pristine surface is not present on the modified surface. The second application, also on the interface catalysis, is on the hydrogen evolution reaction (HER) activity of Cr1-xMoxB2 solid solution. The experiment finds an intriguing canonic-like behaviour of the HER activity as a function of x, and it correlates with the c lattice parameter. We use first-principles calculations to successfully reproduce the nonlinear dependence of the c lattice parameter. Furthermore, we show that hydrogen evolution is promoted when x = 0.6. In the next two applications, we use Wannier functions as a tool to investigate the optical and magnetic properties of materials. We study the optical response of Fe-Co-Al alloys in the THz range. Magnetism can modify the reflection of light from these magnets and this modification strongly depends on the frequency of incoming light in the terahertz range. This finding has potential applications in memory storage devices and the creation of tunable photonic materials. Finally, we study the two-dimensional magnetic material CrI3. We find an unusually large cross-polarized Raman signature of Ag phonon mode in CrI3 by DFT calculation, in agreement with experiments. Surprisingly, the relevant spin-orbit interaction potential originates from iodine atoms, despite magnetism being mostly on chromium atoms. This finding opens the door to exploring new rare-earth-free permanent magnets with large magnetocrystalline anisotropy, or permanent magnets containing earth-abundant elements (such as Sn)