The Bethe-Salpeter Equation Formalism: From Physics to Chemistry

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• The Bethe-Salpeter equation (BSE) formalism is emerging as a powerful computational tool for predicting optical excitations in molecules.
• Accurate prediction of electronic excitations is crucial for understanding molecular properties and designing new materials.

Purpose of the Study:

• To provide a historical overview of the BSE formalism, emphasizing its origins in condensed-matter physics.
• To critically review the strengths and weaknesses of the BSE approach for various chemical applications.
• To highlight the combination of GW approximation and BSE for accurate prediction of optical properties.

Main Methods:

• Utilizing the GW approximation to obtain accurate ionization energies and electron affinities.
• Applying the Bethe-Salpeter equation (BSE) formalism to model UV/vis spectra and calculate singlet excitation energies.
• Comparing the computational cost and accuracy of BSE with time-dependent density-functional theory (TD-DFT).

Main Results:

• The GW-BSE approach yields accurate singlet excitation energies with typical errors of 0.1-0.3 eV.
• BSE offers accuracy comparable to advanced hybrid functionals but avoids the ambiguity of exchange-correlation functional selection.
• BSE effectively addresses challenges like charge-transfer excitations, which are problematic for other methods.

Conclusions:

• The GW-BSE formalism presents an efficient and accurate computational method for predicting optical excitations in molecular systems.
• BSE provides a robust alternative to TD-DFT, offering high accuracy and resolving known limitations.
• Further exploration of BSE's capabilities across diverse chemical scenarios is warranted.