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Accurate Theoretical Assessment of MLCT Transitions in [M(Terpy)2]2+ (M = Fe, Ru, Os) Complexes
Aleksandr A Chamkin1, Elena S Chamkina1
1A.N.Nesmeyanov Institute of Organoelement Compounds of Russian Academy of Sciences, Moscow, Russia.
Abstract:
The present study guides reliable and cost-effective computational approaches to metal-to-ligand charge transfer (MLCT) transitions in model [M(terpy)2]2+ (M = Fe, Ru, Os) complexes relevant to electrochromic applications. We evaluated the performance of multireference perturbation theories (NEVPT2 and CASPT2), DLPNO-STEOM-CCSD, ADC(2), and 44 density functionals within TD-DFT for calculating vertical MLCT excitation energies in these systems. Multireference methods provide the most consistent agreement with experimental absorption maxima. The best theoretical estimates were obtained at the X2C NEVPT(14, 13)/x2c-QZVPPall level (2.368, 2.710, and 2.684 eV for M = Fe, Ru, and Os, respectively). DLPNO-STEOM-CCSD fails for [Fe(terpy)2]2+, presumably due to its multireference character. Among DFT functionals, local meta-GGAs such as r2SCAN offer the best trade-off between accuracy and computational cost.
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