title: Anharmonic effects in the quantum cluster equilibrium method.
abstract: The well-established quantum cluster equilibrium (QCE) model provides a statistical thermodynamic framework to apply high-level ab initio calculations of finite cluster structures to macroscopic liquid phases using the partition function. So far, the harmonic approximation has been applied throughout the calculations. In this article, we apply an important correction in the evaluation of the one-particle partition function and account for anharmonicity. Therefore, we implemented an analytical approximation to the Morse partition function and the derivatives of its logarithm with respect to temperature, which are required for the evaluation of thermodynamic quantities. This anharmonic QCE approach has been applied to liquid hydrogen chloride and cluster distributions, and the molar volume, the volumetric thermal expansion coefficient, and the isobaric heat capacity have been calculated. An improved description for all properties is observed if anharmonic effects are considered.
authors.affiliation: Mulliken Center for Theoretical Chemistry, University of Bonn, Beringstr. 6, D-53115 Bonn, Germany.
authors.forename: Michael
authors.identifier: 0000000301114141
authors.initials: M
authors.lastname: von Domaros
authors.affiliation: Mulliken Center for Theoretical Chemistry, University of Bonn, Beringstr. 6, D-53115 Bonn, Germany.
authors.forename: Eva
authors.identifier: 0000000246700542
authors.initials: E
authors.lastname: Perlt