The simulation of the femtosecond transient absorption pump-probe spectroscopy under the framework of on-the-fly symmetrical quasi-classical/Meyer-Miller dynamics

The theoretical simulation of femtosecond transient absorption pump-probe spectroscopy (TA PP) is crucial to clarify the mechanism of ultrafast nonadiabatic dynamics. The introduction of the doorway-window approximation simplifies the calculation of nonlinear response functions, enabling the simulation of TA PP via the trajectory-based nonadiabatic dynamics approach. In this work, we tried to propose a computational protocol to simulate the TA PP signals of realistic polyatomic systems by combining the doorway-window approximation of the laser-molecular interactions and the on-the-fly symmetrical quasi-classical/Meyer-Miller dynamics (SQC/MM). The underlying physical insight behind the TA PP signals of two molecular systems is analyzed by checking the molecular motions in the nonadiabatic dynamics. This opens a novel and simple approach to simulate the ultrafast spectral signals of the realistic polyatomic systems effectively and efficiently within the framework of the mapping Hamiltonian.