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Initial conditions for surface hopping trajectories from the VSCF-Wigner distribution.
R Cvjetinović1,2, J Odavić3,4, R Ćosić5
1Division of Physical Chemistry, Ruđer Bošković Institute, Bijenička Cesta 54, 10000 Zagreb, Croatia.
This study introduces a new sampling method for trajectory surface hopping (TSH) simulations, using vibrational self-consistent field (VSCF) theory. This approach improves initial condition sampling in photochemical simulations, especially for anharmonic systems.
Area of Science:
- Quantum Chemistry
- Computational Chemistry
- Photochemistry
Background:
- Trajectory surface hopping (TSH) simulations commonly use harmonic Wigner distributions for initial conditions.
- This harmonic approximation fails for anharmonic systems, raising questions about its reliability in photochemical simulations.
Purpose of the Study:
- To develop and assess an anharmonic sampling strategy for TSH simulations.
- To investigate the reliability of harmonic Wigner sampling in the presence of molecular anharmonicity.
Main Methods:
- Introduced a vibrational self-consistent field (VSCF) Wigner quasiprobability distribution.
- Derived analytical expressions for VSCF Wigner sampling in harmonic and distributed Gaussian bases.
- Implemented and tested the method in TSH simulations for malonaldehyde and methyl hydroperoxide.
Main Results:
- VSCF Wigner sampling and harmonic Wigner sampling produced similar results for malonaldehyde, indicating harmonic sampling's continued reliability.
- For methyl hydroperoxide, VSCF Wigner sampling results matched the quantum thermostat approach, offering computational efficiency.
Conclusions:
- Harmonic Wigner sampling can remain reliable even in moderately anharmonic systems.
- VSCF Wigner sampling provides an efficient and improvable alternative for initial-condition sampling in complex photochemical simulations.
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