Performance of the Bethe-Salpeter Equation for Electronic Excitations in First-Row Transition Metal Complexes

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Time-dependent density functional theory (DFT) struggles with accurately describing metal-centered (MC) and charge transfer (CT) transitions in transition metal complexes.
• The choice of exchange-correlation functional in DFT significantly impacts the prediction of excited states.

Purpose of the Study:

• To systematically evaluate the performance of the Green's function-Bethe-Salpeter Equation (BSE@GW) approach for calculating UV-vis spectra of first-row transition metal complexes.
• To compare the accuracy of BSE@GW with DFT for predicting electronic transitions, particularly the interplay between MC and CT states.

Main Methods:

• Application of the Green's function-Bethe-Salpeter Equation (BSE@GW) method.
• Systematic testing on a series of first-row transition metal complexes, including triazacyclononane and Fe(II) complexes with N-heterocyclic carbene ligands.
• Investigation of the influence of ground state geometry and the Tamm-Dancoff approximation.

Main Results:

• BSE@GW calculations show good agreement with experimental UV-vis absorption spectra and transition assignments.
• The BSE@GW method's accuracy is independent of the exchange-correlation functional used in the initial GW calculation.
• The study highlights the challenges DFT faces in correctly ordering MC and CT transitions.

Conclusions:

• BSE@GW is a reliable and robust method for predicting UV-vis spectra of transition metal complexes.
• This approach offers a significant improvement over standard DFT methods for complex electronic transitions.
• The findings provide valuable insights for computational chemists studying the photophysics of transition metal systems.