Time-dependent density-functional study of intermolecular Coulombic decay for 2a$_1$ ionized water dimer

TL;DR

This study employs real-time density functional theory with Ehrenfest dynamics to simulate and analyze the intermolecular Coulombic decay process in water dimers following inner-valence ionization, revealing new dynamical proton transfer pathways.

Contribution

It introduces a combined real-time DFT and Ehrenfest dynamics approach to study ICD in water dimers, capturing both electronic and nuclear motions simultaneously.

Findings

ICD observed in 2a₁ ionized water dimer

Proton exhibits back-and-forth motion during decay

Proton transfer pathways depend on ionization site

Abstract

A real-space, real-time time-dependent density functional theory (RT-TDDFT) with Ehrenfest dynamics is used to simulate intermolecular Coulombic decay (ICD) processes following the ionization of an inner-valence electron. The approach has the advantage of treating both nuclear and electronic motion simultaneously, allowing for the study of electronic excitation, charge transfer, ionization, and nuclear motion. Using this approach, we investigate the decay process for the 2a$_1$ ionized state of the water dimer. For the 2a$_1$ vacancy in the proton donor water molecule, ICD is observed in our simulations. In addition, we have identified a novel dynamical process: at the initial stage, the proton generally undergoes a back-and-forth motion. Subsequently, the system may evolve along two distinct pathways: in one, no proton transfer occurs; in the other, the proton departs again from its original position and ultimately completes the transfer process. In contrast, when the vacancy resides in the proton acceptor water molecule, no proton transfer occurs, and ICD remains the sole decay channel.