Initial conditions for surface hopping trajectories from the VSCF-Wigner distribution

Cvjetinović, Robert; Odavić, Jovan; Ćosić, Rajko; Sapunar, Marin; Došlić, Nađa (2026) Initial conditions for surface hopping trajectories from the VSCF-Wigner distribution. The Journal of Chemical Physics, 164 (11). ISSN 0021-9606

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Official URL: http://doi.org/10.1063/5.0320496

Abstract

In trajectory surface hopping (TSH) simulations, initial conditions are typically generated using harmonic Wigner distributions, which assume independent harmonic normal modes. While this assumption fails for anharmonic systems, it remains unclear under which conditions harmonic Wigner sampling becomes unreliable in photochemical simulations and whether anharmonicity alone is a sufficient criterion for reconsidering the use of harmonic Wigner sampling. In the present study, we introduce a sampling strategy based on vibrational selfconsistent field (VSCF) theory to construct a VSCF Wigner quasiprobability distribution that incorporates anharmonic effects while retaining mode separability. Analytical expressions are derived in both harmonic and distributed Gaussian bases, enabling the implementation in TSH simulations. The method is applied to malonaldehyde and methyl hydroperoxide, which exhibit moderate and strong anharmonicity, respectively. For malonaldehyde, VSCF-based Wigner sampling and harmonic Wigner sampling yield similar results, indicating that harmonic Wigner sampling remains reliable despite the anharmonicity. In methyl hydroperoxide, where torsional motion significantly influences the excited-state character, VSCF Wigner sampling yields results comparable to those of the quantum thermostat approach while offering a computationally efficient and systematically improvable route to initial-condition sampling.

Item Type:

Article

Additional Information:

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in J. Chem. Phys. 164, 114103 (2026) and may be found at https://pubs.aip.org/jcp/article/164/11/114103/3383750/Initial-conditions-for-surface-hopping.

Uncontrolled Keywords:

trajectory surface hopping; phase space sampling; Wigner distribution

Subjects:

NATURAL SCIENCES > Chemistry > Theoretical Chemistry

Divisions:

Division of Physical Chemistry

Projects: