PNNL

Abstract

Calculating accurate free energies of aqueous ionic clusters is important in many areas of chemical physics. A common practice used in ab initio and other methods to determine the cluster free energy is to use a single energetically favorable configuration and then assume the harmonic approximation. In the present study, we compare and contrast harmonic free energies to those determined from anharmonic configurational sampling and how both compare to experiment. It is found that anharmoncity plays a critical role in determining accurate free energies for the clusters underlying ion-induced nucleation. Consequently, energies, geometries, and frequencies obtained using a single or multiple configurations within the harmonic approximation lead to incorrect aqueous cluster thermodynamics.This work was supported by the Office of Basic Energy Sciences of the Department of Energy, in part by the Chemical Sciences Program. The Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.