For more than a few nuclear DOF, solving the TDSE exactly is prohibitively expensive. Depending on the complexity of the molecular system, one may perform the dynamics exactly as dictated by the TDSE or resort to various approximations, such as mixed quantumclassical (MQC) approaches, semi-classical approaches, various approximate master equation approaches (e.g., Lindblad, Redfield, etc.) and approximate wavefunction approaches.