2026/02/12 by Avik Kumar Ojha, John M. Herbert · 1 voice
Chemistry · Materials Science · Physics and Astronomy · #Advanced Chemical Physics Studies #Magnetism in coordination complexes #Photochemistry and Electron Transfer Studies
paper · doi:10.26434/chemrxiv.15000030/v1
openalex publication_date 2026/02/12 · openalex created_date 2026/02/13 · openalex updated_date 2026/07/14
Spin-flip methods provide access to certain electronic states having multireference character while retaining single-reference cost. However, conventional spin-flip time-dependent density functional theory (SF-TDDFT) often suffers from severe spin contamination that may engender inaccurate state ordering or ambiguous state character. For singlet excited states, this is largely rectified by a "mixed-reference" formulation (MRSF-TDDFT), while a spin-adapted formalism (SA-SF-TDDFT) addresses spin contamination in a general way for arbitrary multiplicities. Here, we revisit SA-SF-TDDFT and demonstrate that it significantly improves the agreement with reference data as compared to other variants of SF-TDDFT, and also relative to conventional (spin-conserving) TDDFT. However, the spin-adapted approach exhibits notable limitations in the case of linear and quasilinear doublet radicals, where improvement is less pronounced due to degeneracies in the high-spin quartet reference state.