Ab Initio Investigation Of Ice Under High Pressure

This work is devoted to the study of physical and chemical properties of ice under high pressure from first principles. With the progress in density functional theory (DFT) and its numerical methods, DFT based first-principles calculation has become a general method for the study in condensed matter physics, quantum chemistry and material science. In this dissertation, we carried out detailed research on ice under a wide high pressure rang. The concerned properties include geometry, electronic structure, optical properties, and lattice dynamics.In the first chapter, firstly we introduce the basic structure and the physical and chemical properties of ice and water, with especial emphasis on their unique properties, functions, and the importance of research. Secondly, we summarize the extremely rich phases of ice under high pressure, including their structure and characters; meanwhile, we review the recent progree in the research of ice and water. In the last section, we discuss the necessity and importance of high-pressure study of ice; then we outline the main content of this thesis.In the second chapter, we introduce the basic concepts and computational methods of ab initio calculations based on DFT, including its theoretical framework, the approximation for the exchange-correlation interaction, the pseudopotential method and the plane wave basis sets, the k-point sampling technique for calculation of electronic structure of periodic systems, the test of convergence before calculation of properties and the finite basis set correction. Due to the high pressure condition for the simulations in this work, we also present the theory for the calculation of pressure and the virial theorem. Then we discuss the details of the theory for the calculation of optical properties, the dielectric response theories. Finally, we present the methods and parameters finally used in this work.In the third chapter, we carry out a series of research on ice X, which phase is discovered experimentally under highest pressure and the only one beyond 62GPa. We calculate the pressure dependences of cell dimensions, density, bond lengths, total energy, enthalpy, Fermi energy, band structure, band gap, and the frequencies of phonon modes at G point between 55GPa and 380GPa. Furtherly we evaluate the stability of ice X phase, and predicte the possible phase transition pressures.In the fourth chapter, we check out the super high-pressure phase ice XIIIM, which was theoretically predicted in 1996 by M. Benoit et al but not experimentally confirmed yet. We find a new ice phase with distinct bonding features, the ice XV. Then we discuss detailly about the bonding structures and charge transfers of high-pressure phases of ice, including ice X, ice XIIIM, and ice XV, and compare with the quasi-hcp phase ice XI under ambient pressure and low temperature. Moreover, we analyze the possible phase transition mechanisms from ice X to ice XV beyond 300GPa.In the fifth chapter, we carry out systematical investigation on pressure induced effect on the electronic structures of ice: from the most visualized change of spatial charge density distribution, to the comparison of band structures of high-pressure phases, ice X and ice XV, and the ambient-pressure low temperature phase, iceXI, and to the change of dispersion relations of electronic density of states (DOS) and Partial DOS from specific atoms. Furthermore, we discuss the possibility of metallization of ice. Finally, from the integration of DOS, we analyze the change of orbital hybridization and charge transfers of ice under high pressure.In the final chapter, we discuss in details about the pressure induced change of various optical properties of ice. Firstly, we present the intrinsic mathematical relations among different optical properties and some process we used for the comparison among different phases of ice. Then we present the complete calculation and analysis for the pressure induced variation of optical properties of ice, including dielectric functions, absorption coefficient, reflectivity, electron energy loss spectra, photoconductivity, and refractivities. Finally, the anisotropic optical properties of ice under high pressure are also discussed.