Molecular Dynamic Simulation Of Point Defect In HCP Metals

Point defect is one kind of important crystal defects. Its' creation, motion, interaction, combination and annealing will influence the fundamental physical properties of metal crystal materials. It plays an important role to affect the plasticity, strength, diffusion and other structural sensitive properties, so many experimental, theoretic and computational methods have been developed to study it. Computer simulation has advantage among them due to that it can describe the microcosmic properties and motion of defects directly in details from atomistic scale.In this thesis diffusion of Self-interstial diffusion in HCP zirconium is studied by means of Molecular Dynamic(MD) simulation within NPT system. Ackland's many body inter-atomic potential is employed to describe inter-atomic interaction in HCP zirconium. The size of the simulation crystal cell is 67.89A×65.33A×64.01A, including 11521 atoms. In order to avoid the influence of surface effect, the periodic boundary conditions is employed in simulation, so that the defect can move in infinite space. To control the constant temperature, Nose-Hoover method is employed. A heat bath is used to couple with the system by introducing a fictional dynamical variable. The degrees of freedom of the thermal reservoir are expressed by an extended-system Hamiltonian. Through adjusting the parameter related to frictional mass temperature is controlled. Parrinello-Rahman method is used to control the stress in this thesis, and its idea is to introduce a scale tensor depending upon time, making the volume and shape of the simulation crystal cell change along with time, so that constant-pressure is achieved through the change of the shape.The diffusion coefficients are calculated under condition of 6 constant temperatures from 1000 to 1500 Kelvin and under zero external pressure. The migration energies derived from the relation between diffusion coefficient and temperature are found to be more consistent with Molecular Static calculation thanthe previous study within NVT ensembles. This shows that the effect of stress upon migration energies can't be neglected. To reduce correlation effect along <1120>direction, by increasing temperature the <1120> jumps are interrupted by morejumps perpendicular to (0001) plane. This study will be significance not only in understanding of the effect of microstructure to the properties of material physics and mechanics, but also for the design of defendable materials against radiation damage. It's also important to analyze experimental results.