2 research outputs found
Prediction Challenge: Simulating Rydberg Photoexcited Cyclobutanone with Surface Hopping Dynamics based on Different Electronic Structure Methods
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.Comment: The main manuscript contains 28 pages with 8 figures. The
supplementary material contains 14 pages with 12 figures. In total, the
merged pdf document has 42 pages with 20 figure
Trajectory integration with potential energy discontinuities
Many approximate methods of quantum chemistry yield potential energy surfaces with discontinuities. While clearly unphysical, such features often fall within the typical error bounds of the method, and cannot be easily eliminated. The integration of nuclear trajectories when the potential energy is locally discontinuous is obviously problematic. We propose a method to smooth out the discontinuities that are detected along a trajectory, based on the definition of a continuous function that fits locally the computed potential, and is used to integrate the trajectory across the discontinuity. With this correction, the energy conservation error can be reduced by about one order of magnitude, and a considerable improvement is obtained in the energy distribution among the internal coordinates