Density Functional Theory For Crystallization Of Carbon Dioxide And Ice

Crystal and its crystallization process plays a great important role in scientific investigation and industrial applications. The theoretical investigation of their structures and characters at the micro-scale and is of great importance. CO2 and H2O is two typical crystal. Under the framework of statistical mechanics, we combine the density functional theory with integral equation theory to study structures and characters of crystal and crystal-liquid interface. The main investigations are as follows:(1) Based on the linear structure of CO2, the direct correlation function between different groups was obtained by integral equation theory. Combining the direct correlation function with the connection of the atom in CO2, we presented a three-dimensional density functional theory model to describe CO2 crystal. The crystal-liquid phase equilibria of CO2 was predicted. The microstructure, such as the density distribution of crystal and crystal-liquid interface, was obtained. The macroscopic thermodynamic properties, such as the interfacial tensions and enthalpy of fusion, can be calculated by the microstructure, and the results was consistent with the experimental data.(2) The hydrogen bonding interaction in H2O plays a great important role in the crystallization of H2O. To study the structure and characters of ice, we started our research from the influence of the hydrogen bonding interaction in H2O on the system energy. Combined self-consistent solution of integral equation theory with static renomalization and error function, the direct correlation function reflecting the effects of ver der waals interactions and hydrogen bonding interactions was obtained, and the results was consistent with the experimental data obtained by X-ray diffraction. Compared direct correlation function and radial distribution function calculated under different force field with simulation or experimental data, TTP4P/ice was selected the best force field. Under the force field, the vapor-liquid phase equilibria of H2O was predicted and the results was consistent with the experimental data, suggesting that quantitative expressions of the hydrogen bonding interaction were reasonable and reliable.(3) Based on the structural feature of ice crystal, the construction method of ice crystal by the lattice vectors was presented by added minitrim vectors to the lattice vectors. The construction method can accurately describe the dislocation hexagonal crystal structure of ice. A three-dimensional density functional theory model of ice was presented by applied the effects of hydrogen bonding interactions and configuration of H2O molecule to the expression of free energy function. The crystal-liquid phase equilibria of H2O and the density distribution of crystal and crystal-liquid interface was predicted. The different interfacial tensions can be calculated by the density distribution of crystal-liquid interface, the results was consistent with the experimental data, suggesting that the model can conduct quantitative expressions to crystallization behavior of ice.