All methods described here have been implemented in a development version of GAMESS-US version 30 SEP 2021 (R2 Patch 2). The reference spin-polarized DFTB calculations have been performed using the constrained unrestricted Kohn-Sham algorithm of Tsuchimochi and Scuseria. All calculations have been performed with long-range corrected OB2 set of parameters, using ω = 0.3 long-range separation parameter. The S 0 /S 1 minimum energy crossing points have been searched using the branching update method. For SF-TDDFTB, numerical gradients have been employed for geometry optimizations. For comparison, SF-TDDFT and MRSF-TDDFT calculations have been performed using the same GAMESS version. For all calculations, BH&HLYP functional and Pople's 6-31G(d) basis set has been used. Geodesic interpolation was used to construct reaction paths. 4