Dynamics of the Bulk Hydrated Electron from Many‐Body Wave‐Function Theory

Abstract

The structure of the hydrated electron is a matter of debate as it evades direct experimental observation owing to the short life time and low concentrations of the species. Herein, the first molecular dynamics simulation of the bulk hydrated electron based on correlated wave‐function theory provides conclusive evidence in favor of a persistent tetrahedral cavity made up by four water molecules, and against the existence of stable non‐cavity structures. Such a cavity is formed within less than a picosecond after the addition of an excess electron to neat liquid water, with less regular cavities appearing as intermediates. The cavities are bound together by weak H−H bonds, the number of which correlates well with the number of coordinated water molecules, each type of cavity leaving a distinct spectroscopic signature. Simulations predict regions of negative spin density and a gyration radius that are both in agreement with experimental data.

Picture of the wet electron: a localized transient state in liquid water

“…It is worth noticing in this context that such a disruption of the hydrogen-bond network is a feature that the wet and the hydrated electron have in common. 20,46 This allows us to further clarify the mechanism leading to the formation of the hydrated electron. In fact, we suggest that the role of the wet electron as a precursor is to locally break the hydrogen-bond network in liquid water, in order to "prepare" a suitable site where the subsequent equilibration towards the hydrated electron can occur.…”

“…17,18 It is now well-established that, under thermodynamic equilibrium conditions, the hydrated electron is accommodated in a quasi-spherical electrophilic cavity with a radius of $1.8Å formed upon the re-arrangement of about ve water molecules. 8,[19][20][21] It occupies a s-like ground state within the band gap of the solvent, 17,22 from which it can be excited to p-like states through optical transitions of $1.7 eV. 1 Notwithstanding the large number of studies on the hydrated electron, the atomistic mechanism leading to its formation and the nature of its precursors have remained poorly understood.…”

Simulating the Ghost: Quantum Dynamics of the Solvated Electron

“…Moreover, MP2 provides satisfactory accuracy for the solvated electron, benchmarked against CCSD(T) calculations in clusters [12]. Successful implementation of spin-unrestricted-MP2 (UMP2) energies and forces under periodic boundary conditions has enabled accurate molecular dynamics (MD) of the bulk solvated electron [13,14]. Picosecond-scale MP2-based MD of e − (aq) [14], unprecedented in computational complexity, provided a crucial argument in favor of the cavity structure and against the broadly discussed non-cavity structure [15].…”

Sampling Potential Energy Surfaces in the Condensed Phase with Many‐Body Electronic Structure Methods

“…In the work in reference [62] , MD simulations of the bulk hydratede lectroni nt he periodic cell of 47 water moleculesa t MP2 level with triple-zeta quality basis set are reported for the total of ca. of 5psu sing the RI-GPW-MP2 implementation in the CP2Kprogram.One MD step for such asimulationrequired approximately 20 minutes of wall time on 256 compute nodes (CRAYX C50), consisting of 12 CPUs and 1GPU.…”

“…In the work in reference , MD simulations of the bulk hydrated electron in the periodic cell of 47 water molecules at MP2 level with triple‐zeta quality basis set are reported for the total of ca. of 5 ps using the RI‐GPW‐MP2 implementation in the CP2K program.…”