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Isomeric Equilibria, Nuclear Quantum Effects, and Vibrational Spectra of M+(H2O)n=1−3 Clusters, with M = Li, Na, K, Rb, and Cs, Through Many-Body Representations

preprint
submitted on 04.05.2018 and posted on 07.05.2018 by Marc Riera, Sandra E. Brown, Francesco Paesani

A quantitative characterization of the molecular mechanisms that regulate ion solvation is key to the microscopic understanding of fundamental processes taking place in aqueous environments, with major implications for different fields, from atmospheric chemistry to materials research and biochemistry. This study presents a systematic analysis of isomeric equilibria for small M+(H2O)n clusters, with M = Li, Na, K, Rb, and Cs, from 0 K to 200 K. To determine the relative stability of different isomers of each M+(H2O)n cluster as a function of temperature, replica exchange simulations are carried out at both classical and quantum levels with the recently developed many-body MB-nrg potential energy functions, which have been shown to exhibit chemical accuracy. Anharmonic vibrational spectra are then calculated within the local monomer approximation and found to be in agreement with the available experimental data, providing further support for the accuracy of the MB-nrg potential energy functions. The present analysis indicates that nuclear quantum effects become increasingly im- portant for larger M+(H2O)n clusters containing the heavier alkali metal ions, which is explained in terms of competing ion-water and water-water interactions along with the interplay between energetic and entropic effects. Directly connecting experimental measurements with molecular properties calculated at the quantum mechanical level, this study represents a further step toward the development of a consistent picture of ion hydration from the gas to the condensed phase.

Funding

National Science Foundation

History

Email Address of Submitting Author

fpaesani@ucsd.edu

Institution

University of California San Diego

Country

United States

ORCID For Submitting Author

0000-0002-4451-1203

Declaration of Conflict of Interest

None.

Exports