Spin-Adapted Spin-Flip Tamm-Dancoff Approximation (XSF-TDA) for Singlet-Triplet Gaps in MR-TADF and INVEST Emitters
Abstract
In this work, we assess the recently introduced spin-adapted TDA for spin-flip-down excitations (XSF-TDA) [Mol. Phys. e2631735 (2026)] as a practical approach to this problem. Starting from a high-spin restricted open-shell Kohn--Sham reference, XSF-TDA generates spin-adapted low-spin roots arising from open--open (OO), core--open (CO), open--virtual (OV), and core--virtual (CV) types of spin-flip-down excitations. Across four application sets comprising 243 benchmark cases, XSF-TDA substantially reduces the systematic positive bias observed for TDA and unrestricted spin-flip TDA (USF-TDA). With the B3LYP functional, XSF-TDA reduces the equal-set-weighted macro-MAE relative to USF-TDA from 0.252 eV (0.158 eV) to 0.102~eV (0.056~eV) with the ALDA0 (multicollinear) kernel. Its accuracy is competitive with state-specific ΔDFT and quasiparticle-energy DFT (QE-DFT), while being able to provide deeper mechanistic insight through the response vector. In particular, spin-adapted CV configurations provide selected higher-excitation character that strengthens the OO--CV dynamical-spin-polarization channel, which preferentially stabilizes the singlet states. We also identify an INVEST emitter with appreciable OO--OV mixing, suggesting a possible additional contribution to singlet stabilization when the CV contribution is small. The XSF-TDA method therefore provides practical singlet--triplet gap predictions together with interpretable state analysis for the screening and mechanistic understanding of MR-TADF and INVEST emitters.
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BibTeX
@misc{zhao2026spinadapted,
title = {{Spin-Adapted Spin-Flip Tamm-Dancoff Approximation (XSF-TDA) for Singlet-Triplet Gaps in MR-TADF and INVEST Emitters}},
author = {Hewang Zhao and Hongbo Wang and Liuxin Huang and Yunlong Xiao and Zhendong Li},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.29460},
eprint = {2610.29460},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.29460},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Spin-Adapted Spin-Flip Tamm-Dancoff Approximation (XSF-TDA) for Singlet-Triplet Gaps in MR-TADF and INVEST Emitters
AU - Hewang Zhao
AU - Hongbo Wang
AU - Liuxin Huang
AU - Yunlong Xiao
AU - Zhendong Li
PY - 2026
DA - 2026/10/21
PB - arXiv
DO - 10.48550/arxiv.2610.29460
UR - https://arxiv.org/abs/2610.29460
AB - In this work, we assess the recently introduced spin-adapted TDA for spin-flip-down excitations (XSF-TDA) [Mol. Phys. e2631735 (2026)] as a practical approach to this problem. Starting from a high-spin restricted open-shell Kohn--Sham reference, XSF-TDA generates spin-adapted low-spin roots arising from open--open (OO), core--open (CO), open--virtual (OV), and core--virtual (CV) types of spin-flip-down excitations. Across four application sets comprising 243 benchmark cases, XSF-TDA substantially reduces the systematic positive bias observed for TDA and unrestricted spin-flip TDA (USF-TDA). With the B3LYP functional, XSF-TDA reduces the equal-set-weighted macro-MAE relative to USF-TDA from 0.252 eV (0.158 eV) to 0.102~eV (0.056~eV) with the ALDA0 (multicollinear) kernel. Its accuracy is competitive with state-specific ΔDFT and quasiparticle-energy DFT (QE-DFT), while being able to provide deeper mechanistic insight through the response vector. In particular, spin-adapted CV configurations provide selected higher-excitation character that strengthens the OO--CV dynamical-spin-polarization channel, which preferentially stabilizes the singlet states. We also identify an INVEST emitter with appreciable OO--OV mixing, suggesting a possible additional contribution to singlet stabilization when the CV contribution is small. The XSF-TDA method therefore provides practical singlet--triplet gap predictions together with interpretable state analysis for the screening and mechanistic understanding of MR-TADF and INVEST emitters.
ER -