A quantum lattice-gas model of adsorbed systems is studied to determine the importance of quantum-mechanical processes upon order-disorder transition temperatures. The phase diagram of systems interacting with nearest-neighbor attractive and repulsive potentials is obtained within the Bethe-Peierls approximation. It is found that the transition temperature depends, in order of increasing importance, upon particle statistics, quantum tunneling, and the nearest-neighbor interaction strength. The results are applied to systems of helium adsorbed on graphite.

• Received 9 February 1973

DOI:https://doi.org/10.1103/PhysRevA.8.339