Monitoring Water Clusters “Melt” Through Vibrational Spectroscopy

Abstract

Characterizing structural and phase transformations of water at the molecular level is key to understanding a variety of multiphase processes ranging from ice nucleation in the atmosphere to hydration of biomolecules and wetting of solid surfaces. In this study, state-of-the-art quantum simulations with a many-body water potential energy surface, which exhibits chemical and spectroscopic accuracy, are carried out to monitor the microscopic melting of the water hexamer through the analysis of vibrational spectra and appropriate structural order parameters as a function of temperature. The water hexamer is specifically chosen as a case study due to the central role of this cluster in the molecular-level understanding of hydrogen bonding in water. Besides being in agreement with the experimental data available for selected isomers at very low temperature, the present results provide quantitative insights into the interplay between energetic, entropic, and nuclear quantum effects on the evolution of water clusters from "solid-like" to "liquid-like" structures. This study thus demonstrates that computer simulations can now bridge the gap between measurements currently possible for individual isomers at very low temperature and observations of isomer mixtures at ambient conditions.

Temperature and polarization dependent Raman spectra of liquid H2O and D2O

“…[57,58] Recently reported calculations of the Raman spectrum of liquid water have incorporated Fermi resonance, [59] as was previously done for water clusters. [60]…”

Chemical Accuracy in Modeling Halide Ion Hydration from Many-Body Representations

“…[92] for a recent review). Among existing many-body PEFs for water, MBpol has been shown to correctly predict the vibration-rotation tunneling spectrum of the water dimer [103], the energetics, quantum equilibria, and infrared spectra of small clusters [104,[106][107][108], the structural, thermodynamic, and dynamical properties of liquid water [105,109], the energetics of different ice phases [110], infrared and Raman spectra of liquid water [111][112][113], the vibrational sum-frequency generation spectrum of the air/water interface [114,115], the infrared and Raman spectra of ice I h [116]. More recently, molecular configurations extracted from classical (MD) and quantum pathintegral molecular dynamics (PIMD) simulations with MB-pol have been used to determine the electronic band gap of liquid water, both in the bulk and at the air/water interface, through many-body perturbation theory electronic structure calculations [117].…”

Electron-Hole Theory of the Effect of Quantum Nuclei on the X-Ray Absorption Spectra of Liquid Water

“…NQEs are taken into account via path integral molecular dynamics (PIMD) simulations [43] with the MB-pol manybody potential energy function [44][45][46]. Rigorously built upon the many-body expansion of the interaction energy [42], MB-pol enables the accurate modeling of the properties of water across different phases [47,48], from the dimer [44] and small clusters [49], to liquid water [46,50] and ice [51,52]. We use the self-consistent enhanced static Coulomb-hole and screened exchange (COHSEX) approximation [53] with maximally localized Wannier functions, which greatly enhances the computational efficiency of XAS calculations without compromising the accuracy of the results [54,55].…”