Time-dependent Hole States in Multiconfigurational Time-Dependent Hartree-Fock Approaches: Applications in Photoionization of Water Molecule

TL;DR

This paper develops a multiconfigurational time-dependent Hartree-Fock method to simulate and analyze the ultrafast photoionization of water molecules, introducing a new formalism for defining time-dependent hole states and controlling electronic coherence.

Contribution

It presents a full-dimensional implementation of MCTDHF with a novel TDHS formalism for polyatomic molecules, enabling detailed study of photoionization dynamics and ultrafast control.

Findings

Validated the TDHS formalism against experimental data.

Demonstrated control of electronic coherence using attosecond pulses.

Provided benchmark cross sections for water ionization.

Abstract

By simulating the real-time multielectron wavefunction with the multi-configurational time-dependent Hartree-Fock (MCTDHF) approach, we conduct an \textit{ab initio} study of the single-photon ionization process of a body-fixed water molecule ($\mathrm{H_2O}$) driven by attosecond pulses. To this end, we present a full-dimensional implementation of the MCTDHF method based on one-center expansions, allowing for the simulation of arbitrarily polarized lasers and multi-center polyatomic potentials. With a rigorous definition of the time-dependent hole state (TDHS) using the time-domain generalization of extended Koopmans' theorem (TD-EKT), we derive the reduced ion density matrix within the MCTDHF framework, which inherently encodes the total and channel-resolved photoionization cross sections of $\mathrm{H_2O}$. The cross sections obtained are benchmarked against existing experimental and theoretical results, validating the TDHS formalism. Furthermore, by adjusting the phase delay and intensity ratio of a pair of orthogonally polarized attosecond pulses, we explore the ultrafast control of attosecond coherence between electronic states of $\mathrm{H_2O^+}$.