Zero-point energy conservation in classical trajectory simulations: Application to H₂CO.

Area of Science:

• Chemical Dynamics
• Computational Chemistry
• Quantum Mechanics

Background:

• Zero-point energy (ZPE) violation can compromise quasi-classical trajectory (QCT) simulations, particularly for roaming reactions near bond dissociation thresholds.
• Accurate treatment of ZPE is crucial for correctly determining reaction pathways and product distributions in such systems.

Purpose of the Study:

• To develop and validate a novel approach for preventing ZPE violation in QCT simulations.
• To apply this method to H2CO "roaming" reactions and assess its impact on simulation accuracy and trajectory analysis.

Main Methods:

• A "ZPE-corrected" potential energy surface (PES) was constructed by combining the molecular PES with a global harmonic ZPE surface.
• Shepard interpolation was used to create the global ZPE surface from local harmonic ZPE estimates.
• The ZPE-corrected PES (Veff) was developed with no additional computational cost beyond the original PES (V).

Main Results:

• Four out of five ZPE estimates achieved chemical accuracy (within 4 kJ/mol) for H2CO.
• The ZPE-corrected PES allowed all trajectories to be analyzed, unlike previous methods that discarded a significant portion due to ZPE violation.
• Product rotational distributions were largely unaffected by ZPE correction, validating prior QCT simulations.
• Simulations on the ZPE-corrected PES shifted product kinetic energy release to lower values compared to classical simulations.

Conclusions:

• The developed ZPE-corrected PES offers a robust method for improving the accuracy of QCT simulations for roaming reactions.
• This approach enhances the reliability of trajectory analysis by including all simulated paths.
• Classical simulations of kinetic energy release should be interpreted with caution due to potential ZPE-related inaccuracies.