Quantum cluster equilibrium theory of liquids: molecular clusters and thermodynamics of liquid ethanol

Abstract

Quantum cluster equilibrium (QCE) theory is presented for liquid ethanol. The cluster equilibria that dictate phase composition are determined by the rigorous techniques of quantum statistical thermodynamics in the canonical ensemble, based on the ab initio partition function. The characteristic features of the supramolecular clusters which comprise the QCE model are discussed in terms of binding energies, geometries, cooperativity and charge transfer. The validity of the resulting QCE model is demonstrated by comparison with experimental ther-modynamic data: Clausius—Clapeyron pressure/temperature dependence and the specific heat. At room temperature, neat, liquid ethanol consists of approximately equal parts of monomer, cyclic tetramer and cyclic pentamer clusters.