The Work-Hamiltonian Connection and the Usefulness of the Jarzynski Equality for Free Energy Calculations

TL;DR

This paper clarifies the relationship between work, Hamiltonian changes, and free energy, demonstrating that the Jarzynski equality remains useful for free energy calculations when properly understood and applied.

Contribution

It resolves recent debates by clarifying free energy definitions and confirms the Jarzynski equality's validity for molecular pulling experiments.

Findings

Different free energy definitions cause confusion in applicability.

The Jarzynski equality can reliably produce free energy profiles.

Explicit demonstration with molecular pulling experiments confirms its usefulness.

Abstract

The connection between work and changes in the Hamiltonian for a system with a time-dependent Hamiltonian has recently been called into question, casting doubt on the usefulness of the Jarzynski equality for calculating free energy changes. In this paper, we discuss the relationship between two possible definitions of free energy and show how some recent disagreements regarding the applicability of the Jarzynski equality are the result of different authors using different definitions of free energy. Finally, in light of the recently raised doubts, we explicitly demonstrate that it is indeed possible to obtain physically relevant free energy profiles from molecular pulling experiments by using the Jarzynski equality and the results of Hummer and Szabo.