Abstract
We have extended the thermodynamic perturbation cycle approach to compute thermodynamic properties of systems with nonadditive potentials. A rapid iterative method was developed and tested by application to systems of water microclusters of alkali metal cations and halogen anions interacting by means of a model potential incorporating polarization. The perturbation cycle calculations are in agreement with the results of direct calculation as long as both initial and final microclusters are unambiguously stable. For marginally stable cationic microclusters, e.g. Rb(H2O)+6 or Cs(H2O)+5, the perturbation cycle approach appears to provide more reliable estimates of thermodynamic properties. Transmutation entropy estimates entail substantial uncertainty, even for transitions between stable microclusters. They are in fair agreement with those of other theoretical studies but differ noticeably from the experimental values.