2-in-1 Phase Space Sampling for Calculating the Absorption Spectrum of the Hydrated Electron

Abstract

The investigation of vibrational effects on absorption spectrum calculations often employs Wigner sampling or thermal sampling. While Wigner sampling incorporates zero-point energy, it may not be suitable for flexible systems. Thermal sampling is applicable to anharmonic systems, yet it treats nuclei classically. The application of Generalized Smoothed Trajectory Analysis (GSTA) as a post-processing method allows for the incorporation of nuclear quantum effects, combining the advantages of both sampling methods. We demonstrate this approach in computing the absorption spectrum of the hydrated electron. Theoretical exploration of the hydrated electron and its embryonic forms, such as water cluster anions, poses a significant challenge due to the diffusivity of the excess electron and the continuous motion of water molecules. In many previous studies, the wave nature of atomic nuclei is often neglected, despite the substantial impact of nuclear quantum effects on thermodynamic and spectroscopic properties, particularly for hydrogen atoms. In our studies, we examine these nuclear quantum effects for the excess electron in various water systems. We obtained structures from mixed classical-quantum simulations for water cluster anions and the hydrated electron, incorporating the quantum effects of atomic nuclei with the filtration of the classical trajectories. Absorption spectra were determined at different theoretical levels. Our results indicate significant nuclear quantum effects, redshift and broadening of the spectra for hydrated electron systems. This study demonstrates the applicability of GSTA to complex systems, providing insights into nuclear quantum effects on energetic and structural properties.