Dynamical transition orbitals: A particle-hole description in real-time TDDFT dynamics

Area of Science:

• Quantum Chemistry
• Computational Physics
• Theoretical Chemistry

Background:

• Linear-response time-dependent density functional theory (LR-TDDFT) is standard for electronic excitation studies.
• Real-time time-dependent density functional theory (RT-TDDFT) simulates non-equilibrium electron dynamics but lacks a clear particle-hole description.
• Kohn-Sham wavefunctions in RT-TDDFT are invariant under unitary transformations, offering gauge freedom.

Purpose of the Study:

• To extend the concept of natural transition orbitals (NTOs) to RT-TDDFT.
• To develop a particle-hole description for analyzing electron dynamics in RT-TDDFT.
• To introduce a new gauge, dynamical transition orbitals (DTOs), for RT-TDDFT.

Main Methods:

• Propagating Kohn-Sham single-particle wavefunctions in RT-TDDFT simulations.
• Exploiting gauge freedom of wavefunctions via unitary transformations.
• Projecting time-dependent Kohn-Sham wavefunctions onto occupied/unoccupied subspaces to construct NTOs.
• Forming DTOs as linear combinations of hole/particle orbitals.

Main Results:

• A novel framework using DTOs is established for RT-TDDFT.
• DTOs provide a useful particle-hole description for dynamic electron transitions.
• The framework successfully analyzes RT-TDDFT simulations of optical excitation and electronic stopping.

Conclusions:

• The developed DTOs offer a powerful tool for interpreting RT-TDDFT simulations.
• This approach enhances the study of non-equilibrium electron dynamics and particle-hole transitions.
• The method is applicable to various dynamic processes in electronic systems.