Work

Quantum Thermochemistry: Multistructural Method with Torsional Anharmonicity Based on a Coupled Torsional Potential

Year: 2013

Type: article

Abstract: We present a new approximation for calculating partition functions and thermodynamic functions by the multistructural method with torsional anharmonicity (MS-T). The new approximation is based on a reference potential with torsional barriers obtained from a calculation that includes local torsional coupling. By comparing to a fully coupled classical rotational-torsional partition function evaluated as a numerical phase space integral, the method is shown to provide improved accuracy in the classical limit. Quantum effects, which are most important at low temperatures, are included based on the harmonic approximation (which can be upgraded to a quasiharmonic approximation, that is, harmonic formulas with effective frequencies). Calculations were performed for six molecules (ethanol, 1-butanol, hexane, isohexane, heptane, and isoheptane), one radical (1-pentyl radical), and the saddle point structures of a hydrogen abstraction reaction (hydroxyl plus ethanol) to illustrate the difference between the new coupled-potential MS-T approximation and the original uncoupled-potential MS-T approximation. The new method improves the agreement with experimental results of calcuated thermodynamic functions for 1-butanol, hexane, isohexane, and heptane.

Source: Journal of Chemical Theory and Computation

DOI: 10.1021/ct3010722

Authors: Jingjing Zheng, Donald G. Truhlar

Institutions: University of Minnesota, Minnesota Supercomputing Institute

Language: English

Topic: Advanced Chemical Physics Studies

Subfield: Atomic and Molecular Physics, and Optics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: hybrid

Estimated APC paid: $4,500

Funder: U.S. Department of Energy