Parameter-free calculation of response functions in time-dependent density-functional theory.

Area of Science:

• Computational Materials Science
• Quantum Chemistry
• Condensed Matter Physics

Background:

• Calculating optical absorption spectra with excitonic effects is crucial for understanding material properties.
• The Bethe-Salpeter equation is a standard but computationally intensive method for these calculations.

Purpose of the Study:

• To establish and implement a fully ab initio method for calculating optical absorption spectra, including excitonic effects.
• To achieve results of the same precision as the Bethe-Salpeter equation without its computational complexity.

Main Methods:

• Utilizing time-dependent density-functional theory (TD-DFT).
• Developing new, parameter-free exchange-correlation kernels (f(xc)).
• Investigating the role of the response function in conjunction with f(xc).

Main Results:

• The new method accurately reproduces excitonic effects in optical spectra.
• Results for bulk Silicon (Si) and Silicon Carbide (SiC) show excellent agreement with experimental data.
• The precision of the results is comparable to those obtained using the Bethe-Salpeter equation.

Conclusions:

• A novel, efficient TD-DFT-based method has been developed for calculating optical absorption spectra.
• The method simplifies the calculation of excitonic effects, offering a viable alternative to the Bethe-Salpeter equation.
• This advancement provides a more accessible route for accurate optical property predictions in materials science.