All-electron ab initio Bethe-Salpeter equation approach to neutral excitations in molecules with numeric...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• The GW+Bethe-Salpeter equation (BSE) formalism is a powerful tool for calculating optical gaps and spectra in solids, and predicting neutral excitations in molecules.
• Accurate prediction of molecular excitations is crucial for understanding chemical processes and designing new materials.

Purpose of the Study:

• To develop and validate an all-electron GW+BSE implementation for molecular systems using numeric atom-centered orbital (NAO) basis sets.
• To assess the accuracy and convergence properties of the new method for predicting low-lying excitation energies.

Main Methods:

• Implementation of the all-electron GW+BSE formalism utilizing numeric atom-centered orbital (NAO) basis sets.
• Benchmarking calculations on a set of small organic molecules (Thiel's set) to compare with literature data.
• Investigation of basis set convergence using valence correlation consistent NAO and standard NAO basis sets with augmentation functions.

Main Results:

• The all-electron GW+BSE method with NAOs reproduces literature reference data with high precision (approx. 1 meV).
• Excellent convergence to the complete basis set limit is demonstrated for various NAO basis sets.
• A cost-effective "tier2+aug2" augmented NAO basis set is identified as efficient for production calculations.
• Similar convergence properties are observed for linear-response time-dependent density functional theory (LR-TDDFT) within the NAO formalism.

Conclusions:

• The developed all-electron GW+BSE approach with NAOs provides an accurate and efficient method for calculating molecular excitation energies.
• The study recommends specific NAO basis sets for reliable and computationally feasible calculations.
• The findings extend the applicability of accurate electronic structure methods to molecular systems using a versatile basis set approach.