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

Abstract

The structure of the hydrated electron is amatter of debate as it evades direct experimental observation owingtothe short life time and lowc oncentrations of the species.H erein, the first molecular dynamics simulation of the bulk hydrated electron based on correlated wave-function theory provides conclusive evidence in favor of ap ersistent tetrahedral cavity made up by four water molecules,and against the existence of stable non-cavity structures.Such acavity is formed within less than ap icosecond after the addition of an excess electron to neat liquid water,w ith less regular cavities appearing as intermediates.T he cavities are bound together by weak HÀH bonds,the number of whichcorrelates well with the number of coordinated water molecules,e acht ype of cavity leaving ad istinct spectroscopic signature.S imulations predict regions of negative spin density and ag yration radius that are both in agreement with experimental data.

Simulating the ghost: quantum dynamics of the solvated electron

“…Most of the trajectories localized the solvated electron and formed a cavity within 1 ps. This localization dynamics featuring the delocalized, the pre-solvated, and the cavity structures consecutively is in agreement with both experiment and previous ab initio MD simulations 6 , 7 , 16 , 24 . Furthermore, the inclusion of NQEs activates a novel diffusion mechanism involving the formation of a twin cavity (Fig.…”

“…1 g). Spin density distributions reveal the characteristic negative density regions next to H atoms 16 , 25 . The radial distribution functions (RDFs) of H and O atoms relative to the spin density center (restricted to single-cavity structures, see Supplementery Methods for the definition, and the results for D 2 O) provide a more quantitative structural characterization of the cavity, as shown in Fig.…”

“…Moreover, MP2 provides satisfactory accuracy for the two- and three-body interactions for water 13 and solvated electron in clusters 14 , benchmarked against CCSD(T) calculations. 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 15 , 16 . Picosecond-scale MP2-based MD of e − (aq) 16 , unprecedented in computational complexity, provided a crucial argument in favor of the cavity structure and against the broadly discussed non-cavity structure 17 .…”

Below Band Gap Formation of Solvated Electrons in Neutral Water Clusters?

“…The former time scale (τ 1 VBE = 220 fs) has been assigned to fast solvent reorganization and electron localization into a cavity with size on the order of a few Å, which is further stabilized by slow solvent reorganization (τ 2 VBE = 1.6 ps). 8 , 30 , 34 Very similar time scales are also retrieved from the sequential kinetics model ( Figure 2 b). The relaxed hydrated electron (DAS 3 , green line) is formed in <2 ps, through the transient states represented by DAS 1 (blue line) and DAS 2 (red line).…”

“…These conduction band electrons relax rapidly toward the bottom of the conduction band by fast energy dissipation through electron scattering on time scales of several 10 fs. 15 , 31 , 60 − 63 Localization from the bottom of the conduction band to interband trapped states likely takes place on time scales faster than ∼100 fs, 15 , 25 , 30 , 34 followed by slower solvent rearrangement and geminate recombination.…”