Phase changes in Lennard-Jones mixed clusters with composition ArnXe6−n (n=,1,2)

We have carried out parallel tempering Monte Carlo calculations on the binary six-atom mixed Lennard-Jones clusters, ArnXe6−n (n=0,1,2). We have looked at the classical configurational heat capacity CV(T) as a probe of phase behavior. All three clusters show a feature in the heat capacity in the region of 15–20K. The Ar2Xe4 cluster exhibits a further peak in the heat capacity near 7K. We have also investigated dynamical properties of the Ar2Xe4 cluster as a function of temperature using molecular dynamics. We report the interbasin isomerization rate and the bond fluctuation parameter obtained from these calculations. At 7K, the isomerization rate is on the order of 0.01ns−1; at 20K, the isomerization rate is greater than 10ns−1. Furthermore, at 7K, the bond fluctuation parameter is less than 3%; at 20K, it is in the range of 10–15% (depending on the sampling time used). Using this information, together with Monte Carlo quenching data, we assign the 15–20K feature in the heat capacity to a solid-liquid phase change and the 7-K peak to a solid-solid phase change. We believe this is the smallest Lennard-Jones cluster system yet shown to exhibit solid-solid phase change behavior.