Using constant-temperature simulations, an investigation was made of the effect of an alternating uniaxial external stress upon vacancy migration in a face-centered cubic argon crystal in which the atoms interacted with each other via a 12-6 Lennard-Jones potential. The crystal was confined between two smooth walls which interacted with the atoms through a similar Lennard-Jones potential, and an alternating stress field was exerted by moving both of the walls inwards (compressive) or outwards (expansive) sinusoidally with a frequency of 93MHz. Periodic boundary conditions were imposed in the other two directions. The amplitude of the sinusoidal wall movement along the [100] axis corresponded to a strain of 0.0138 and a stress of about 15MPa. At this small strain amplitude, the vacancy jump frequency, when averaged over a full stress cycle, had a value similar to that in the unstressed bulk crystal. However, the vacancy jump frequency was higher with a larger proportion of jumps being in planes normal to the stress axis, during the expansive half-cycle than during the compressive half cycle. Thus, the jump behaviour was anisotropic under stress, and this anisotropy was opposite for the two half-cycles.

Molecular Dynamics Study of Vacancy Diffusion in a Forced Lennard-Jones System. Balaji, S., Abinandanan, T.A., Ayappa, K.G., Chandrasekhar, N.: Philosophical Magazine A, 2000, 80[2], 301-10