**Molecular Dynamics Simulations of Grain-Boundary Diffusion for
Varying Tilt Angle Geometries**

S. J. Plimpton, in Atomic Scale Calulations of Structure in Materials, edited by M. S. Daw and M. A. Schluter, MRS Proceedings 193, Pittsburgh, PA, 1990, p 333-336.

The effect of structure and geometry on grain boundary self-diffusion is investigated. Using static structures found by relaxation techniques (conjugate gradients) as starting points for a molecular dynamic simulation of a bicrystal model, diffusion coefficients and activation energies are calculated for (100) fcc Al and bcc $\alpha$-Fe tilt boundaries. These quantities are derived by monitoring the mean-squared displacement of atoms in the grain boundary region as the simulation progresses and as the temperature of the simulated solid is changed. The angular, directional, and structural dependence of the simulated diffusion are discussed and compared to experimental measures and theoretical predictions. The implementation of the molecular dynamics algorithm on a parallel supercomputer is also briefly discussed to illustrate the performance benefits these computers make possible.

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