Probing Interfacial Effects on Ionization Energies: The Surprising Banality of Anion-Water Hydrogen Bonding at the Air/Water Interface

Abstract

Liquid microjet photoelectron spectroscopy is an increasingly common technique to measure vertical ionization energies (VIEs) of aqueous solutes, although the interpretation of these experiments is subject to questions regarding sensitivity to bulk versus interfacial solvation environments. Here, we compute aqueous-phase VIEs for a set of inorganic anions, some of which partition preferentially at the air/water interface, using a combination of molecular dynamics simulations and electronic structure calculations. The results are in excellent agreement with experiment, regardless of whether the simulation data are restricted to ions at the air/water interface or to those in bulk liquid water. Although the computed VIEs are sensitive to ion-water hydrogen bonding, we find that the short-range solvation structure is sufficiently similar in the bulk and interfacial environments that it proves impossible to discriminate between the two on the basis of the VIE, a conclusion that has important implications for the interpretation of liquid-phase photoelectron spectroscopy. More generally, analysis of the simulation data suggests that partitioning of soft anions at the air/water interface is largely a second (or third) solvation shell effect, arising from disruption of water-water hydrogen bonds and not from significant changes in first-shell anion-water hydrogen bonding. <br>

Natural Charge-Transfer Analysis: Eliminating Spurious Charge-Transfer States in Time-Dependent Density Functional Theory via Diabatization, with Application to Projection-Based Embedding

“…84 In practice, this selfconsistent reaction-field (SCRF) problem is implemented using a polarizable continuum formalism, 84 although direct solution of eq 6 in three-dimensional space could also be used. [85][86][87][88] The result in either case is a one-electron potential v SCRF added to the Fock matrix for subsystem A:…”

“…This multilayer embedding is accomplished by solving the generalized Poisson equation using the combined density γ̃ A ( r )⊕γ B ( r ) from the embedding calculation, where ϵ­( r ) constitutes a sharp dielectric interface (cavity) surrounding the atomistic region . In practice, this self-consistent reaction-field (SCRF) problem is implemented using a polarizable continuum formalism, although direct solution of eq in three-dimensional space could also be used. − The result in either case is a one-electron potential v SCRF added to the Fock matrix for subsystem A : Inserting this into eq facilitates self-consistent optimization of γ ̃ A within the embedding potential of both the explicit and implicit environments. Rather than obtaining v SCRF exclusively from the density optimized at the lower level of theory, eq allows the continuum to respond to changes in the high-level subsystem density matrix and thus represents a fully self-consistent implementation of continuum boundary conditions for projection-based embedding.…”