On-The-Fly Dynamics of Multiconfigurational Wave Packets by a Semiclassical Method

An on-the-fly, trajectory-based semiclassical scheme for the time propagation of multiconfigurational nuclear wave packets (MCWPs) is proposed. This enables MCWP time propagation without a prefitted global potential energy surface, in contrast to variational approaches such as the widely used multiconfiguration time-dependent Hartree (MCTDH), while retaining multimode couplings and favorable scaling. Comparisons with the matrix-product-state MCTDH method for formaldehyde, together with on-the-fly infrared spectra of benzene benchmarked against experiment, show that accurate wave packet propagation can be achieved within a semiclassical framework. The approach also extends to transitions between electronic states; for benzene fluorescence, incorporating Herzberg-Teller coupling reproduces the characteristic vibronic structure.