  Using a recently developed approach to represent ab initio based force fields
by a neural network potential, we perform molecular dynamics simulations of
lead telluride (PbTe) and cadmium telluride (CdTe) crystals. In particular, we
study the diffusion of a single cation interstitial in these two systems. Our
simulations indicate that the interstitials migrate via two distinct
mechanisms: through hops between interstitial sites and through exchanges with
lattice atoms. We extract activation energies for both of these mechanisms and
show how the temperature dependence of the total diffusion coefficient deviates
from Arrhenius behaviour. The accuracy of the neural network approach is
estimated by comparing the results for three different independently trained
potentials.
