Quantum simulation study of the hydrated electron

Abstract

An excess electron in a sample of classical water molecules at room temperature has been simulated using path integral techniques. The electron–water interaction is modeled by a pseudopotential with effective core repulsion and further terms for the Coulomb interaction and polarization effects. Various discretizations of the electron path, up to 1000 points, are examined. The charge distribution of the electron is found to be compact and to occupy a cavity in the water, in agreement with the conventional picture. The solvation shell structure is similar to that of relatively large solvated atomic anions, but the radial electron-solvent correlations are largely smeared out due to fluctuations of the electronic density distribution. In parts of the simulation the structure of the first solvation shell corresponds on the average to the structure proposed for hydrated electrons by Kevan. The computed solvation energy and the estimated energy of the first optical excitation agree reasonably well with experimental data.

A Drude-model approach to dispersion interactions in dipole-bound anions

“…8,21,22,35,62,148 It was long believed that theoretical methods allowing for the electrostatic interactions, and perhaps also, polarization of the water molecules by the excess electron, were adequate for describing (H 2 O) n -species. 21,22,[74][75][76][77]105 Within an ab initio electronic structure framework, this would lead one to believe that the Hartree-Fock method provides a good zeroth-order description of the wavefunction of the anion and of the electron binding energies of these species. This expectation has also served as the basis of several one-electron model approaches that have been developed for describing an excess electron interacting with water.…”

“…[88][89][90][91][92] Yet, even the nature of an excess electron in bulk water remains controversial. [93][94][95][96][97][98][99][100][101][102][103] Although the long-held view is that an excess electron in bulk water is trapped in an approximately spherical cavity, [104][105][106][107] giving the so-called hydrated electron, Domcke and coworkers have proposed that the excess electron is actually associated with a H 3 O species. 100 (H 2 O) n -clusters have also received considerable attention from the experimental and theoretical communities.…”

“…43,161,162 Geometries with the positive ends of the monomer dipoles pointing toward one another and with the excess electron "trapped" in the resulting attractive potential in the interior of the cluster are often referred to as "solvated-electron" species. The hydrated electron 103,105,107 is probably the most famous solvated-electron species. (Here we have assumed that the commonly accepted picture of the hydrated electron -in which the electron is bound in an approximately spherical cavity surrounded by water molecules with "free" OH groups pointing toward the center of the cavity -is correct.…”

Hydration dynamics in water clusters via quantum molecular dynamics simulations

“…A notable problem concerns the structure of the hydrated electron. The more or less consensus, localized cavity structure 36,37,38 has been challenged by an alternative model, 39 a non-cavity type ("inverse-plum" 40 ) electron distribution for the bulk hydrated electron. As another structural issue, there is still no agreement on where the excess electron is localized relative to the nuclear frame in water clusters, i.e.…”

“…One-electron mixed quantum-classical simulations have been proved to be valuable in investigating and interpreting hydrated electron properties. 18,38,49,50,51,52,53 In the present paper, we apply QCMD simulations for the relaxation dynamics of water clusters. Two main non-equilibrium scenarios will be modeled and investigated in detail.…”