Beyond TD-DFT: Assessing the Bethe-Salpeter Equation within the GW Approximation for Absorption Properties

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Time-dependent density functional theory (TD-DFT) is widely used for predicting optical absorption properties due to its balance of efficiency and accuracy.
• Limitations of TD-DFT include challenges in achieving both quantitative accuracy and reliable structure-property trend prediction.
• The GW/Bethe-Salpeter equation (GW/BSE) approach is emerging as a powerful alternative for optical property calculations.

Purpose of the Study:

• To comprehensively evaluate and compare the performance of TD-DFT against GW/BSE methods for predicting one-photon (1PA) and two-photon absorption (2PA) properties.
• To assess the accuracy and reliability of eigenvalue self-consistent GW (evGW/BSE) and single-shot G0W0/BSE approaches.
• To determine the suitability of these computational methods for modeling optical properties in a diverse set of fluorophores.

Main Methods:

• Calculations were performed using TD-DFT and GW/BSE (evGW/BSE and G0W0/BSE) methods.
• The resolution-of-identity (RI) approximation was employed.
• Results were benchmarked against resolution-of-identity second-order approximate coupled-cluster (RI-CC2) calculations.

Main Results:

• TD-DFT remains effective for predicting one-photon absorption (1PA).
• Both evGW/BSE and G0W0/BSE methods demonstrated superior performance for two-photon absorption (2PA) compared to TD-DFT.
• GW/BSE approaches showed lower absolute errors, better agreement with qualitative trends, and overcame the accuracy-trend trade-off limitations of TD-DFT.

Conclusions:

• GW/BSE methods, specifically evGW/BSE and G0W0/BSE, are highly promising for accurate optical property modeling, particularly for two-photon absorption (2PA).
• These methods offer reliable quantitative predictions and robust structure-property correlations, surpassing TD-DFT in these aspects.
• The findings support the broader adoption of GW/BSE frameworks for computational studies of optical properties.