  Non-adiabatic dynamics simulations have become a standard approach to explore
photochemical reactions. Such simulations require underlying potential energy
surfaces and couplings between them, calculated at a chosen level of theory,
yet this aspect is rarely assessed. Here, in combination with the popular
trajectory surface hopping dynamics method, we use a high-accuracy XMS-CASPT2
electronic structure level as a benchmark for assessing the performances of
various post-Hartree-Fock methods (namely CIS, ADC(2), CC2 and CASSCF) and
exchange-correlation functionals (PBE, PBE0, CAM-B3LYP) in a TD-DFT/TDA
context, using the isomerization around a double bond as test case. Different
relaxation pathways are identified, and the ability of the different methods to
reproduce their relative importance and timescale is discussed. The results
show that multi-reference electronic structure methods should be preferred,
when studying non-adiabatic decay between excited and ground states. If not
affordable, TD-DFT with TDA and hybrid functionals, and ADC(2) are efficient
alternative, but overestimate the non-radiative decay yield and thus may miss
deexcitation pathways.
