Fortunately, photoisomerization of the PSB3 molecule that is considered herein involves only the two lowest singlet states. Instead of using a fully spin-adapted version of SF-TDDFT, for which the analytic gradient is not yet available, we instead aim to obtain only approximately spin-pure S 0 and S 1 states. To achieve this, we simply enforce that the two open-shell Slater determinants in Fig. (b) must form a singlet configuration state function when solving the SF-TDDFT eigenvalue equations, meaning that their coefficients must be equal in magnitude and opposite in sign. For PSB3, the S 0 and S 1 states that we obtain in this way typically have Ŝ2 < 0.5 and are thus easy to distinguish from triplet states. As discussed below, we do observe some exceptions, in which S 1 is significantly spin contaminated (with Ŝ2 ≈ 1); this occurs in cases where one of the single bonds in PSB3 is significantly twisted. However, the manifold of excited states is sparse enough that we are nevertheless able to perform consistent NMD simulations via trajectory surface-hopping, without resort to state-tracking algorithms.