Nonadiabatic coupling vectors are required for the aFSSH simulations and are available in analytic form in Q-Chem, for both LR-TDDFT and SF-TDDFT. Whereas calculation of the derivative couplings is sometimes (incorrectly) perceived as being significantly more expensive than analytic gradients, in reality the calculation of h IJ for TDDFT adds only about 10% overhead on top of the cost of computing the gradients ∇R E I (R) and ∇R E J (R).