Halide Ion Micro-Hydration: Structure, Energetics, and Spectroscopy of Small Halide–Water Clusters

Abstract

<div> <div> <div> <p>Replica exchange molecular dynamics simulations and vibrational spectroscopy calculations are performed using halide-water many-body potential energy functions to provide a bottom-up analysis of the structures, energetics, and hydrogen-bonding arrangements in X−(H2O)n=3−6 clusters, with X = F, Cl, Br, and I. Independently of the cluster size, it is found that all four halides prefer surface-type structures in which they occupy one of the vertices in the underlying three-dimensional hydrogen-bond networks. For fluoride-water clusters, this is in contrast with previous reports suggesting that fluoride prefers interior-type arrangements, where the ion is fully hydrated. These differences can be ascribed to the variability in how various molecular models are capable to reproduce the subtle interplay between halide-water and water-water interactions. Our results thus emphasize the importance of a correct representation of individual many-body contributions to the molecular interactions for a quantitative description of halide ion hydration. </p> </div> </div> </div>

MB-Fit: Software Infrastructure for Data-Driven Many-Body Potential Energy Functions

“…Given the demonstrated accuracy of the MB-pol PEF for water, [58][59][60][61] and the TTM-nrg and MBnrg PEFs for ions in water 92,95,[100][101][102][103][104][105]107 and various molecular fluids, 97,98 we believe that MB-Fit can open the door to routine, predictive computer simulations of small molecules in the gas, liquid, and solid phases, including, but not limited to, the modeling of molecular clusters, solvation structure and thermodynamics, heterogeneous processes at air/liquid and air/solid interfaces, molecular crystals, and phase diagrams.…”

“…99 When used in computer simulations, the TTM-nrg and MB-nrg PEFs consistently provide remarkable agreement with experimental data, which is effectively quantitative in the case of the MB-nrg PEFs. 97,98,[100][101][102][103][104][105]107 In the most general form, the TTM-nrg and MB-nrg PEFs approximate the MBE of Eq. 1 as…”

“…99 When employed in computer simulations, the MB-nrg PEFs have been shown to consistently provide remarkable agreement with experimental data for both gas-phase and condensed-phase systems. [100][101][102][103][104][105][106][107] Here, we present MB-Fit, a complete software infrastructure for the automated development of TTM-nrg and MB-nrg PEFs for generic molecules. Besides providing a complete array of computational tools for generating the necessary training and test sets, performing the required quantum mechanical (QM) calculations, and fitting the TTM-nrg and MB-nrg PEFs, MB-Fit is seamlessly integrated with the MBX software, 108 a many-body energy/force calculator in both finite and periodic boundary conditions, which enables computer simulations with both TTM-nrg and MB-nrg PEFs, currently supporting LAMMPS 109 and i-PI 110 .…”