Symmetric quasi-classical dynamics with quasi-diabatic propagation scheme

We apply a recently developed quasi-diabatic (QD) scheme to the symmetric quasi-classical (SQC) approach for accurate quantum dynamics propagation. By using the adiabatic states as the QD states during a short-time quantum dynamics propagation, the QD scheme allows for directly interfacing the diabatic SQC method with commonly used adiabatic electronic structure calculations, thus alleviating any non-trivial theoretical efforts to reformulate SQC in the adiabatic representation. Furthermore, the QD scheme ensures a stable propagation of the dynamics and allows using a much larger time step compared to directly propagating SQC dynamics in the adiabatic representation. This is due to the fact that the QD scheme does not explicitly require non-adiabatic couplings that could exhibit highly peaked values during non-adiabatic dynamics propagation. We perform the QD-SQC calculations with a wide range of model non-adiabatic systems to demonstrate the accuracy of the proposed scheme. This study opens up the possibility for combining accurate diabatic quantum dynamics methods such as SQC with any adiabatic electronic structure calculations for non-adiabatic on-the-fly propagations.