Linear-response TDDFT is widely used for excited states but suffers from spin contamination in spin-conserving and spin-flip channels. Spin-adapted RPA was developed using tensor equation-of-motion and applying the Wigner-Eckart theorem with tensor decoupling. Casting the RPA Fock matrix and kernels as energy derivatives gives a TDDFT extension. To restore spin-component degeneracy, we use hybrids combining HF exchange with spin-unpolarized pure XC parts. Benchmarks, Cr2 dissociation, and phenol O-H conical intersections demonstrate the method.
@article{arxiv.2605.19361,
title = {Spin-Adapted TDDFT},
author = {Xiaoyu Zhang and Tai Wang},
journal= {arXiv preprint arXiv:2605.19361},
year = {2026}
}