How to obtain reaction free energies from free-energy profiles

Dietschreit, Johannes C. B.; Diestler, Dennis J. und Ochsenfeld, Christian (2022): How to obtain reaction free energies from free-energy profiles. In: Journal of Chemical Physics, Bd. 156, Nr. 11, 114105

Abstract

For chemical reactions that occur via the rearrangement of atoms from a configuration about one minimum (reactant, R) of the potential energy surface (PES) to a configuration about another minimum (product, P), an exact relation between the Helmholtz reaction free energy (delta F-RP) and the free-energy profile (FEP) can be derived. Since the FEP assumes a form similar to that of the PES along the minimum energy path between R and P, there is an unfortunate tendency to regard the FEP as the free-energy analog of the minimum energy path and consequently to equate delta F-RP to the difference between the values of the FEP at the minima corresponding to R and P. Analytic treatments of one- and two-dimensional models are presented that show how this mistaken idea leads to errors. In effect, treating the FEP by analogy with the minimum energy path neglects the role of entropy. The FEP is a function of a collective variable (CV), which must be chosen to describe the course of the rearrangement consistently with the exact relation between delta F-RP and the FEP. For large systems of common interest, the PES is often so complex that a straightforward way of choosing a CV is lacking. Consequently, one is forced to make an educated guess. A criterion for judging the quality of the guess is proposed and applied to a two-dimensional model. (C) 2022 Author(s).

• Dokumententyp: Zeitschriftenartikel
• Fakultät: Chemie und Pharmazie > Department Chemie
• Themengebiete: 500 Naturwissenschaften und Mathematik > 540 Chemie
• ISSN: 0021-9606
• Sprache: Englisch
• DFG: Gefördert durch die Deutsche Forschungsgemeinschaft (DFG) - 325871075