The shock compression of condensed matter can be effe ctively dealt with by molecular dynamics,and has been applied to many fields of science.However,there is large scale computation in molecular dynamics,so it is very important to develop the parallel and optimizing algorithm.An approach to the parallelization and optimization is proposed on the NOW (Network of Workstation),and has got the satisfactory result.

The two-dimensional molecular dynamics calculation is used to simulate ejection and damage phenomena. The intermolecular force is described by Morse potential. Molecules are initially located in equilibrium position and spaced so that the free surface has an angle shape for simulating real machined surface. Shock wave may be produced by motion of first layer of molecules (piston) or by impact of flyer of molecules. When the disturbance arrives at free surface, the boundary molecules start to run away from it with large velocity and the inside damage begins. The ratio of ejection velocity to the surface one changes from 1 to 3 and it is dependent on the shock strenth, surface angle and material property. When the semiangle is bigger than 60°, the boundary molecules can not run away from others, i.e. the ejection disappears. It also disappears when shock strength is lower than a limit value dependent ont he surface angle and material. In the both ejection and jetless cases the calculation shows the process of microvoid formation and growth.

The propagation of shock wave and it's reflection at free surface in two-dimensional lattice are considered and calculated by method of molecular dynamics. This lattice simulates the (1,0,0) plane for face centered cubic (f.c.c) or the (1,1,0)plane for body centered cubic(b.c.c).In the range of our calculation (u_p=10-75×10⁴cm/sec), the oscillation of particle velocity is'nt decrescent. The shock wave velocity is a linear function of average particle velocity. After reflection, the average particle velocity near free surface is equal to twice the piston velocity approximately, which agrees with macroscopic phenomena. The particles at outer-most layer of free surface, get the large value of velocity and go away from this surface. It is also similar to the macroscopic phenomena of ejection. At the later stage of expansion, the particles in the interial region may lose connection between them, that corresponds to the microscopic fracture.