Quantum kinetic energy and isotope fractionation in aqueous ionic solutions

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 HPO${}_4^{2-}$ ions perturbs the competition between quantum effects in liquid water and impacts their local solvation structures.

References in corpus (16)

• Separable Dual Space Gaussian Pseudo-potentials
• Competing quantum effects in the dynamics of a flexible water model
• Nuclear quantum effects in water
• i-PI 2.0: A Universal Force Engine for Advanced Molecular Simulations
• Ab initio thermodynamics of liquid and solid water
• i-PI: A Python interface for ab initio path integral molecular dynamics simulations
• Efficient first-principles calculation of the quantum kinetic energy and momentum distribution of nuclei
• Quantum delocalization of protons in the hydrogen bond network of an enzyme active site
• Efficient methods and practical guidelines for simulating isotope effects
• Unraveling quantum mechanical effects in water using isotopic fractionation
• Effect of quantum nuclear motion on hydrogen bonding
• Quantum fluctuations and isotope effects in ab initio descriptions of water
• Direct Measurement of Competing Quantum Effects on the Kinetic Energy of Heavy Water upon Melting
• Inverse Temperature Dependence of Nuclear Quantum Effects in DNA Base Pairs
• Probing defects and correlations in the hydrogen-bond network of ab initio water
• Nuclear quantum effects in water exchange around lithium and fluoride ions