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Quantum kinetic energy and isotope fractionation in aqueous ionic solutions

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Abstract

At room temperature, the quantum contribution to the kinetic energy of a water molecule exceeds the classical contribution by an order of magnitude. The quantum kinetic energy (QKE) of a water molecule is modulated by its local chemical environment and leads to uneven partitioning of isotopes between different phases in thermal equilibrium, which would not occur if the nuclei behaved classically. In this work, we use ab initio path integral simulations to show that QKEs of the water molecules and the equilibrium isotope fractionation ratios of the oxygen and hydrogen isotopes are sensitive probes of the hydrogen bonding structures in aqueous ionic solutions. In particular, we demonstrate how the QKE of water molecules in path integral simulations can be decomposed into translational, rotational and vibrational degrees of freedom, and use them to determine the impact of solvation on different molecular motions. By analyzing the QKEs and isotope fractionation ratios, we show how the addition of the Na+, Cl and HPO42− ions perturbs the competition between quantum effects in liquid water and impacts their local solvation structures.

Graphical abstract: Quantum kinetic energy and isotope fractionation in aqueous ionic solutions

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Article information


Submitted
29 Nov 2019
Accepted
08 Jan 2020
First published
08 Jan 2020

Phys. Chem. Chem. Phys., 2020, Advance Article
Article type
Paper

Quantum kinetic energy and isotope fractionation in aqueous ionic solutions

L. Wang, M. Ceriotti and T. E. Markland, Phys. Chem. Chem. Phys., 2020, Advance Article , DOI: 10.1039/C9CP06483D

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