Reference CC3 Excitation Energies for Organic Chromophores: Benchmarking TD-DFT, BSE/GW, and Wave Function Methods

Area of Science:

• Computational Chemistry
• Theoretical Spectroscopy
• Photochemistry and Photophysics

Background:

• Accurate calculation of vertical transition energies is crucial for understanding and designing organic chromophores.
• Existing computational databases for these energies are limited, especially for large organic molecules.
• Benchmarking various theoretical methods is essential for reliable predictions in dye chemistry.

Purpose of the Study:

• To expand the QUEST database with highly accurate vertical transition energies for large organic chromogens.
• To benchmark the performance of lower-order wave function approaches and time-dependent density-functional theory (TD-DFT) methods.
• To evaluate a wide range of exchange-correlation functionals and the Bethe-Salpeter equation (BSE) formalism.

Main Methods:

• High-level coupled-cluster calculations (CC3 and CCSDT) were performed to obtain reference vertical excitation energies.
• A series of lower-order wave function methods (e.g., CC2, ADC(2)) and TD-DFT with various functionals were benchmarked.
• Bethe-Salpeter equation (BSE) calculations using G0W0 and evGW quasiparticle energies were also assessed.

Main Results:

• Over 120 new highly accurate singlet and triplet vertical excitation energies were computed for molecules like anthraquinone and BODIPY.
• CC2 and ADC(2.5) emerged as the most accurate and computationally efficient methods for large systems.
• Several TD-DFT functionals (BMK, M06-2X, CAM-B3LYP, etc.) and double hybrid functionals showed good performance, comparable to CC2.

Conclusions:

• CC2 and ADC(2.5) provide a reliable balance of accuracy and computational cost for vertical transition energies in large organic chromogens.
• Specific TD-DFT functionals and double hybrids offer competitive accuracy, making them viable alternatives for certain applications.
• The study provides valuable reference data for the QUEST database, aiding future research in dye chemistry and materials science.