Calculation of the Gibbs energy of the reaction OH- • (H2O)n-1+H2O=OH- • (H2O)n by the Monte-Carlo method

The energy and the Gibbs energy of the reaction OH-.(H2O)(n-1) + H2O = OH-.(H2O)(n) are calculated by the Monte-Carlo method with a large canonical ensemble for n = 1, ..., 20. The ion-water nonpair interaction potential was obtained by numerical fitting of calculated Gibbs energy and entropy of (H2O)(n) clusters (n = 1, ..., 5) to experimental ones. A good fit to experiment both of the internal energy and the Gibbs energy can be obtained in terms of a model allowing for nonpair interaction. It is shown that constructing an ion-water interaction potential without allowance for the entropy factor can lead to considerable errors in the Gibbs energy of cluster formation and in the nucleation rate.