To clarify, classical dynamics here generally refers to dynamics that abide by Newton's equation of motion, no matter what kind of FF/potential is provided. Unlike most classical MD working with non-reactive FF, sampling on reactive space requires using reactive potentials, like reactive FF, semi-empirical methods or QM methods (i.e., AIMD), etc. The main problem in classical dynamics is the low chances of climbing over the energy barrier and to capture rare events. A common strategy is running dynamics at a sufficiently high temperature to increase chances to reach high-energy rare events. For example, Meuwly group applied langevin dynamics at 1000K for initial data sampling for Diels-Alder and hydrogen transfer reactions . Another common strategy to cover reactive PES is to set the intial structures around rare events so that the MD trajectories naturally slide down to cover the reaction path trajectories. For example, Duarte group initialized MD simulations from near-TS area . Similar to this strategy, quasi-classical trajectory simulations are also applied to sample near-MEP surface starting from TS . The main difference from classical dynamics is the initial condition in QCT is based on QM hessian and normal modes of QM TS. Normal modes that are orthogonal to imaginary frequency modes make QCT oscillating in directions orthogonal to MEP and thus guarantee a comprehensive coverage around MEP rather than strictly following MEP.