Monte Carlo computer simulation was used to investigate the impurity form of the correlation factor i.e. the form of the correlation factor used to process results of the experimental isotope effect. The model chosen was the honeycomb lattice gas at 50% occupation with repulsive interactions. The impurity form turned out to be a rather poor approximation for any temperature with the situation becoming very serious at temperatures below the order-disorder temperature.

Diffusion in the Lattice Gas II: the Isotope Effect. L.Zhang, G.E.Murch: Defect and Diffusion Forum, 1997, 141-142, 59-64