A photoexcitation of a molecule produces a nonstationary nuclear wavepacket in an electronically excited state, initiating ultrafast dynamics that is likely to drive the wavepacket to explore different configurations in the excited states. This process ultimately leads in most instances to non-radiative de-excitation via internal conversion towards lower-lying states through conical intersections. Internal conversions are prototypical examples of the breakdown of the Born-Oppenheimer approximation, as the kinetic coupling between electrons and nuclei is responsible for nonadiabatic electronic transitions. Therefore, NAMD relies on the combination of approaches to capture the quantum dynamics of the nuclei coupled to ground and excited electronic states, whose effect enters in terms of energies, forces and couplings which are determined -usually on-the-fly -either via ab-initio/semiempirical techniques or by employing analytical expressions. The fine balance between accuracy and efficiency guides the choice of the level of theory used for the simulations.