Computation of Molecular Ionization Energies Using an Ensemble Density Functional Theory Method

Area of Science:

• Theoretical Chemistry
• Computational Quantum Chemistry
• Spectroscopy

Background:

• Accurate computation of ionization energies and Dyson orbitals is crucial for understanding molecular electronic structure.
• Existing methods can be computationally expensive, limiting their application in dynamic processes.
• Simulating time-resolved photoelectron spectroscopy requires efficient theoretical tools.

Purpose of the Study:

• To develop and implement a novel computational methodology for fast calculation of ionization energies and Dyson orbitals.
• To enable on-the-fly calculations during nonadiabatic molecular dynamics simulations.
• To provide a theoretical framework for simulating time-resolved photoelectron spectroscopy.

Main Methods:

• Integration of the extended Koopmans theorem (EKT) with the state-interaction state-averaged spin-restricted ensemble-referenced Kohn-Sham (SI-SA-REKS or SSR) method.
• Leveraging analytical energy gradients from SSR to recycle intermediate quantities for EKT calculations.
• Application of the new methodology to compute ionization energies and Dyson orbitals for various molecular systems.

Main Results:

• Demonstrated fast computation of ionization energies and Dyson orbitals in ground and excited electronic states.
• Successfully applied the method to strongly correlated systems, dissociating bonds, and conical intersections.
• Established the capability for on-the-fly evaluation of ionization energies and probabilities during molecular dynamics.

Conclusions:

• The developed EKT-eDFT methodology offers a significant speed-up for calculating ionization properties.
• This approach opens new avenues for theoretical simulations of time-resolved photoelectron spectroscopy.
• The method is robust and applicable to complex chemical systems and phenomena.