We present a detailed study of the decoherence correction to surface hopping that was recently derived from the exact factorization approach. Ab initio multiple spawning calculations that use the same initial conditions and the same electronic structure method are used as a reference for three molecules: ethylene, the methaniminium cation, and fulvene, for which nonadiabatic dynamics follows a photoexcitation. A comparison with the Granucci−Persico energy-based decoherence correction and the augmented fewest-switches surface-hopping scheme shows that the three decoherence-corrected methods operate on individual trajectories in a qualitatively different way, but the results averaged over trajectories are similar for these systems.
A surface-hopping
algorithm recently derived from the exact factorization
approach, SHXF [Ha et al. J. Phys. Chem. Lett.
2018, 9, 1097], introduces an additional
term in the electronic equation of surface hopping that couples electronic
states through the quantum momentum. This term not only provides a
first-principles description of decoherence, but here we show it is
crucial to accurately capture nonadiabatic dynamics when more than
two states are occupied at any given time. Using a vibronic coupling
model of the uracil cation, we show that the lack of this term in
traditional surface-hopping methods, including those with decoherence
corrections, leads to failure to predict the dynamics through a three-state
intersection, while SHXF performs similarly to the multiconfiguration
time-dependent Hartree quantum dynamics benchmark.
Extending the Shin-Metiu two-electron Hamiltonian, we construct a new Hamiltonian with effective singlet-triplet couplings. The Born-Oppenheimer electronic potentials and couplings are obtained for different parameters, and the laser-free dynamics is calculated with the full Hamiltonian and in the adiabatic limit. We compare the dynamics of the system using nuclear wave packets for different numbers of Born-Oppenheimer potentials and vibronic wave packets on a full 3-dimensional (two electron coordinates plus one nuclear coordinate) grid. Using strong fields, we show that it is possible to dynamically lock the spin state of the system by decoupling the singlet-triplet transition via a nonresonant dynamic Stark effect in the adiabatic limit. Although a similar spin-locking mechanism is observed in the dynamics of vibronic wave packets, multiphoton ionization cannot be neglected leading to the breakdown of the control scheme.
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