The controversy over the relaxation mechanism of photoexcited thymine such as S 1 -trapping, S 2 -trapping, and S 1 &S 2 -trapping has been recently resolved by our NAMD study using MRSF-TDDFT. Our study supports the S 1 -trapping mechanism with two lifetimes, τ 1 =30±1 fs and τ 2 =6.1±0.035 ps, quantitatively consistent with the recent time-resolved experiments. Accordingly, upon photo-excitation to the S 2 (ππ * ) state, thymine undergoes an ultrafast (ca. 30 fs) S 2 → S 1 internal conversion through (IC) a conical intersection (CI 21,BLA ) and resides around the minimum on the S 1min