Equilibrium, stability, and density anomalies in a lattice model with core-softening and directional bonding

The cluster-variation method has been used to investigate the phase behavior, thermal expansion characteristics, and stability limits of the Bell-Meijer lattice model; the model includes directional bonding and second neighbor repulsion. Both of these mechanisms are in principle capable of stabilizing open ground states and can therefore give rise to negative thermal expansion. A canonical implementation of the natural iteration solution technique facilitated the calculation of metastable states and stability limits. The four types of phase behavior previously found by Van Royen and Meijer 34 have been mapped as a function of the relative strength of the second neighbor repulsion and the bonding interaction over a wide range of parameter space