  This research examines the nonadiabatic dynamics of cyclobutanone after
excitation into the n-3s Rydberg S2 state. It stems from our contribution to
the Special Topic of the Journal of Chemical Physics to test the predictive
capability of computational chemistry against unseen experimental data.
Decoherence-corrected fewest-switches surface hopping (DC-FSSH) was used to
simulate nonadiabatic dynamics with full and approximated nonadiabatic
couplings. Several simulation sets were computed with different electronic
structure methods, including a multiconfigurational wavefunction (MCSCF)
specially built to describe dissociative channels, multireference semiempirical
approach, time-dependent density functional theory, algebraic diagrammatic
construction, and coupled cluster. MCSCF dynamics predicts a slow deactivation
of the S2 state (10 ps), followed by an ultrafast population transfer from S1
to S0 (<100 fs). CO elimination (C3 channel) dominates C2H4 formation (C2
channel). These findings radically differ from the other methods, which
predicted S2 lifetimes 10 to 250 times shorter and C2 channel predominance.
These results suggest that routine electronic structure methods may hold low
predictive power for the outcome of nonadiabatic dynamics.
