Using density-corrected DFT to understand density-driven and functional-dependent errors in ab initio simulations of the hydrated electron

The hydrated electron, an excess electron in liquid water, plays a crucial
role in a plethora of chemical processes, motivating extensive research
efforts to characterize its structure, dynamics, and reactivity in
solution. Recent theoretical approaches for understanding this intriguing
object have involved ab initio simulations based on density functional
theory (DFT). Although ab initio DFT methods allow for the study of
hydrated electron reactivity, they also suffer from significant
self-interaction error (SIE). Density-corrected DFT (DC-DFT) provides a
framework to mitigate SIE; the method minimizes density-driven errors by
replacing the self-consistent density associated with a given density
functional with the Hartree-Fock (HF) density. Here, we investigate how
the use of density correction affects the calculated properties of
DFT-simulated hydrated electrons. First, we analyzed charge delocalization
in a system consisting of a model octahedral hydrated electron water
cluster (the so-called Kevan structure) along with a spatially separated
sulfur atom. We show that the use of density correction indeed reduces SIE
in comparison to a standard DFT global hybrid functional. We then
propagate molecular dynamics trajectories of the hydrated electron using
DC-DFT, where we find that DC further localizes electron density in the
cavity region, a signature of reduced charge delocalization.
Unfortunately, the decreased radiation of gyration of the spin density and
corresponding tightening of the local solvation structure from density
correction causes predicted observables to deviate further from
experimental measurements than when density correction is not employed.
This indicates that the difficulties with DFT to simulate hydrated
electrons are primarily due to the inherent approximations in DFT rather
than density-driven errors due to SIE.