  Heat capacity curves as functions of temperature were calculated using Monte
Carlo methods for the series of Ne_(13-n)Ar_n clusters (0 <= n <= 13). The
clusters were modeled classically using pairwise additive Lennard-Jones
potentials. The J-walking (or jump-walking) method was used to overcome
systematic errors due to quasiergodicity. Substantial discrepancies between the
J-walking results and those obtained using standard Metropolis methods were
found. Results obtained using the atom-exchange method, another Monte Carlo
variant for multi-component systems, also did not compare well with the
J-walker results. Quench studies were done to investigate the clusters'
potential energy surfaces. Only those Ne-Ar clusters consisting predominately
of either one or the other component had lowest energy isomers having the
icosahedral-like symmetry typical of homogeneous 13-atom rare gas clusters;
non-icosahedral structures dominated the lowest-energy isomers for the other
clusters. This resulted in heat capacity curves that were very much different
than that of their homogeneous counterpart. Evidence for coexistence behavior
different than that seen in homogenous clusters is also presented.
