First, in addition to exploiting the numerical techniques described above, we also introduce new methods that appear to greatly improve the numerical stability of the time-dependent QTM calculations. This is an extremely important development from the perspective of practical, widespread adoption of the approach as a generic robust computational tool. Second, we aim to extend the time-dependent formalism to nonadiabatic processes in the same manner as for adiabatic processes. However, in a "standard" formulation of nonadiabatic dynamics, the effect of several electronic states is accounted for via the inclusion of multiple potential energy surfaces (PESs), and couplings among them; 41 this picture is fundamentally different from adiabatic dynamics, where a single electronic state, and thus a single PES, contributes to the "classical force" guiding nuclear dynamics (in addition to the quantum force already discussed). Note that wavefunction-based nonadiabatic quantum trajectory dynamics have certainly been considered in the past. However, these were done in a standard Born-Huang (or related) representation of nonadiabatic dynamics involving multiple PES components-which, for technical reasons, poses a source of fundamental difficulties in the interacting trajectory-based context. Accordingly, in this work, we instead invoke the exact factorization formalism in combination with the interacting quantum trajectories approach presented above [ 36,38]. The exact factorization yields nuclear dynamics under the effect of a single time-dependent classical force accounting for the electronic excited states, thereby avoiding the aforementioned technical difficulty.