Multiple-configuration versus single-configuration thermodynamic quantities for water and some other clusters

Abstract At present, clusters are most usually theoretically studied as local energy minima on potential hypersurfaces; quite typically a manifold occurrence of such minima on one hypersurface is encountered. The cluster isomerism proved in this theoretical way has substantial consequences for comparisons of theory with experiment as well as for interpretation and prediction purposes. It leads to differentiation between two classes of quantities, namely multiple- and single-configuration characteristics. This approach is significant for any structure-dependent property; nevertheless, it has been developed most extensively for thermodynamic characteristics of cluster formation. These problems are illustrated with water clusters, (CO 2 ) 2 − and other systems, particular attention being paid to the heat capacity term. More generally, even contributions of clusters of different dimensions can be considered for some quantities. The approach is applied to interpretation of the saturated pressure of steam, and temperature increase of relative cluster populations under the saturation condition is rationalized.