Investigation On Liquid Structure And Dynamic Properties Of Several Materials By The First-principle Method

The importance of searching for the liquid structure of material has been drawn great attention. Because the experiments show that the advantage and disadvantage of material performance depend on their microstructure. To seek the fundamental reason, we have to trace back the melt structure of material changing with temperature.In this paper, we adopt the first-principle molecular dynamics method to simulate microstructure and dynamic properties of several materials and to search the changing structure of pure metal after quenching the temperature and to identify the structural differences of liquid and super-cooled states, and to provide the theoretical basis of glass formation.We study the structure properties of silica at high temperature 3500K. We get the pair correlation function in good agreement with other methods. The diffusion coefficient has been obtained by the mean square displacement curves. The Van-Hove function information describes the atomic motion is non-Gaussians.It is usually hard to get amorphous for pure metallic materials on experiments. We study the process of rapid quenching of the liquid iron at 2200K through 2000K,1800K, 1600K to 1400K and then obtain the statistical analysis of the pair distribution function, mean square displacement, correlation and the Voronoi polyhedra at the temperature equilibrium state. The results show that as temperature decreases, the cage effect is significant and the time of the cage effect is earlier. The average coordination number of atoms is gradually increased. This is in consistent with the situation that the polyhadra of 10,11 reduced and polyhadra of 13,14,15 increased in liquid.To obtain the specific mechanism of the evolution of liquid Ni microstructure during the process of the solidification, and hoping to get the new informations on their structure changes between liquid state and super-cooled state, we simulate the system of Ni at 4000K,3000K,2000K and 1000K. The results show that with decreasing temperature, the cage effects are significant and the platform will be longer. The distribution of polyhedra have centralized, the polyhedra of in 12,13,14 have increased and the polyhedra of 16 have disappeared in liquid.