  This paper provides the first ab-initio on-the-fly example of using the
Quasi-Diabatic (QD) scheme for non-adiabatic simulations with diabatic dynamics
approaches. The QD scheme provides a seamless interface between diabatic
quantum dynamics approaches and {\it adiabatic} electronic structure
calculations. It completely avoids additional theoretical efforts to
reformulate the equation of motion from diabatic to adiabatic representation,
or construct global diabatic surfaces. This scheme enables many recently
developed diabatic quantum dynamics approaches for ab-inito on-the-fly
simulations, providing the non-adiabatic community a wide variety of approaches
(such as the real-time path integral method and symmetric quasi-classical
approach) beyond the well-explored methods (like trajectory surface-hopping or
ab-initio multiple-spawning). The QD scheme also enables using realistic test
cases (like ethylene photodynamics) that go beyond simple model systems to
assess the accuracy and limitation of recently developed quantum dynamics
approaches.
