On the Relationship Between Hydrogen-Bonding Motifs and the 1b1 Splitting in the X-ray Emission Spectrum of Liquid Water

Abstract

The split of the 1<i>b</i><sub>1</sub> peak observed in the X-ray emission (XE) spectrum of liquid water has been the focus of intense research over the last two decades. Although several hypotheses have been proposed to explain the origin of the 1<i>b</i><sub>1</sub> splitting, a general consensus has not yet been reached. In this study, we introduce a novel theoretical/computational approach which, combining path-integral molecular dynamics (PIMD) simulations carried out with the MB-pol potential energy function and time-dependent density functional theory (TD-DFT) calculations, correctly predicts the split of the 1<i>b</i><sub>1</sub> peak in liquid water and not in crystalline ice. A systematic analysis in terms of the underlying local structure of liquid water at ambient conditions indicates that several different hydrogen-bonding motifs contribute to the overall XE lineshape in the energy range corresponding to emissions from the 1<i>b</i><sub>1</sub> orbitals, which suggests that it is not possible to unambiguously attribute the split of the 1<i>b</i><sub>1</sub> peak to only two specific structural arrangements of the underlying hydrogen-bonding network.

The Anomalies and Local Structure of Liquid Water from Boiling to the Supercooled Regime as Predicted by the Many-Body MB-pol Model

“…By contrast, these MB-pol results provide support to a recent theoretical analysis of the x-ray emission spectrum of liquid water showing that the observed 1b 1 splitting cannot be attributed to any specific hydrogen-bonding topology. 61 Importantly, we note that the structural results presented in Fig. 3 provide a possible explanation for the anomalous slower structural relaxation we observed at 208 K compared to 198 K (Figs.…”

Uptake of N2O5 by aqueous aerosol unveiled using chemically accurate many-body potentials

“…Contrary to common neural network models, these many-body potentials have an explicit representation for longrange interactions, which can be important at extended interfaces 25 . For example, it has been shown that MB-pol 26,27 yields quantitative accuracy for a variety of molecular properties across water's phase diagram [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] including at the water-vapor interface 44 . Extensions of this modeling framework to describe mono-atomic ions and small molecules in aqueous solutions as well as generic mixtures of molecules have been recently realized [45][46][47][48][49] .…”

The Anomalies and Local Structure of Liquid Water from Many-Body Molecular Dynamics Simulations

“…By contrast, these MB-pol results provide support to a recent theoretical analysis of the x-ray emission spectrum of liquid water showing that the observed 1b 1 splitting cannot be attributed to any specific hydrogen-bonding topology. 49 In summary, we used MD simulations with the many-body MB-pol model to monitor the evolution of several thermodynamic response functions of liquid water, from the boiling point down to deeply supercooled temperatures. The agreement provided by MB-pol with key aspects of experimental data for the isothermal compressibility, heat capacity, and liquid density over the entire temperature range lends credence to the underlying molecular-level picture of liquid water, which progressively and continuously transforms from a system containing several hydrogen-bonding topologies at high temperature to a nearly perfect tetrahedral liquid below 230 K. MB-pol also predicts maxima in the isothermal compressibility and heat capacity at ∼223 K, which provides support to recent experimental measurements that located the maxima in both thermodynamic response functions at ∼229 K. Our results also help corroborate the experimental observation of a density minimum in confined water, and suggest that such a phenomenon may also exist in bulk supercooled liquid water.…”