Development And Application Of Localized Orbitals Based First-principles Package

With the rapid development of supercomputers and the advances of numerical algo-rithms, the first-principles method based on density functional theory (DFT) is becom?ing more and more important in the field of condensed matter physics, materials science,chemistry and biology. There are two important fields in the development of density functional theory: one is the development of more refined approximations for exchange-correlation functionals, of which the purpose is to get more accurate results; the other is the development of numerical methods, which are designed for large-scale calcula-tions. With the development of plane wave basis set and pseudopotential, it becomes possible to study the electronic structure of systems with hundreds of atoms using den-sity functional theory. While the emergence and continuous development of numerical atomic orbital basis makes it possible to accurately calculate large-scale systems. First-principles package has played an important role in the development of density functional theory: on the one hand, it is a necessary platform for the new developed algorithm; on the other hand, it is the link between density functional theory and scientific applica-tions. Our group has developed a first-principles package, named Atomic-orbital Based Ab-initio Computation at UStc (ABACUS), from scratch, which is developed to per-form large-scale DFT simulations using linear combinations of atomic orbitals (LCAO)method . During the last five years, the author has been focusing on the development of new algorithms and the optimization of performance in ABACUS, and applied ABA-CUS to relevant scientific problems. In the process of implementing new algorithms and optimizing the performance of ABACUS, the author gained a comprehensive and clear understanding of the structure of the first-principles software.The achievements in the thesis are: 1. We implemented the Pulay-Kerker charge mixing method and the second-order charge extrapolation method, which will acceler-ate the convergence rate of electron iteration and improve the computational efficiency.2. We optimized the algorithm of charge density matrix calculation, which speeds up a few times. We optimized the grid integral in ABACUS, which speeds up about 4?5 times. We implemented the interface between ABACUS and ELPA with our cooperator,and the matrix diagonaliztion speeds up 3?5 times. 3. After repeated performance and benchmark test, we obtain an accurate, stable and efficient first-principles package. We released the package in the form of open source, hoping to cooperate with others to pro-mote the development and application of first-principle code packages. 4. We applied first-principles calculations with ABACUS on the equilibrium isotope fractionation in the field of geochemistry, and obtained results consistent with the experiment. 5. We carried out first-principles calculations with ABACUS on the kinetic fractionation of isotopes. We found that the isotope kinetic fractionation factor ? are not sensitive to the temperature if it is well above the liquidus, but can be significantly smaller when temperature is close to the liquidus. In addition, the ? value may depend on the chemi-cal composition of the melts. 6. We applied first-principles calculations with ABACUS to study deuterium diffusion in liquid tin. We found faster diffusion of deuterium in liquid tin than in liquid lithium, and the tin diffusivity and structures are insensitive to the inserted deuterium at temperatures and concentrations considered. Our simulations suggested that liquid tin can be used as an alternative candidate for plasmafacing com-ponent with its retention of hydrogen isotopes significantly differs from liquid lithium.