Numerical QTMs that are referred to as synthetic are those that propagate the wavefunction's hydrodynamic fields (density and phase) along the quantum trajectories, and deduce trajectory dynamics at each time step from those field values. We refer the reader to the book of Wyatt for an excellent review. A major numerical benefit of such a trajectorybased representation in a Lagrangian frame is the fact that one essentially ends up with a moving grid (i.e., the trajectories themselves) that follows the probability flow. Using the moving grid to "sample" the nuclear configuration space in this manner thus allows one to substantially reduce the number of grid points needed to accurately describe, for instance, scattering processes. In many practical instances, use of QTMs rather than wavefunctionbased methods may be reasonably expected to provide better-than-exponential scaling with system dimensionality-whereas fixed-grid methods, in contrast, are always characterized by exponential scaling.