Monte Carlo calculations have been used to study the effect of temperature on the orientational ordering of classical octopoles on two-dimensional triangular net with toroidal boundary conditions. In the absence of crystal field effects three distinct phases have been observed: a high temperature disordered phase, an intermediate phase of undetermined structure, and a low temperature ordered phase. When the crystal field is sufficiently strong that the octopoles sit as stable tripods on the surface free to rotate only about the axis normal to the surface, only two phases are observed, a high temperature disordered phase and a low temperature ordered phase. The relevance of the models to the registered adsorbed phase of methane on graphite is discussed and the experimental evidence is reviewed.
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O’Shea et al. (1979) studied this question.