Identifying Electronic Modes by Fourier Transform from δ-Kick Time-Evolution TDDFT Calculations

Area of Science:

• Computational Chemistry
• Quantum Mechanics
• Materials Science

Background:

• Time-dependent density-functional theory (TDDFT) is crucial for calculating electron excitations in molecules and clusters.
• Two main TDDFT approaches exist: linear-response (LR-TDDFT) and real-time (RT-TDDFT).
• LR-TDDFT requires extensive empty states, posing challenges for large systems, while RT-TDDFT avoids this but lacks direct spectral feature information.

Purpose of the Study:

• To demonstrate an efficient method for extracting transition densities from RT-TDDFT.
• To assess the technical feasibility of using Fourier transforms of induced density for spectral analysis in complex systems.
• To validate the extracted transition densities against LR-TDDFT results.

Main Methods:

• Utilized a single delta-kick time-evolution calculation within the RT-TDDFT framework.
• Applied Fourier transform to the time-dependent induced density to identify spectral features.
• Compared results with traditional LR-TDDFT calculations and standard RT-TDDFT simulations.

Main Results:

• Successfully extracted transition densities for optically allowed excitations efficiently, even in complex systems like noble metals.
• Validated the accuracy of the RT-TDDFT-derived transition densities through comparison with LR-TDDFT.
• Confirmed the technical feasibility of the Fourier-transform method for general RT-TDDFT applications.

Conclusions:

• The delta-kick RT-TDDFT approach provides an efficient and accurate alternative for calculating electron excitations, especially for large systems.
• Fourier transform of induced density is a viable and powerful tool for analyzing spectral features in RT-TDDFT.
• This method enhances the utility of RT-TDDFT for understanding electronic excitations in complex materials.