Cumulative isomerization probability studied by various transition state wave packet methods including the MCTDH...

Area of Science:

• Quantum Chemistry
• Chemical Dynamics
• Computational Spectroscopy

Background:

• Calculating reaction probabilities is crucial for understanding chemical reactions.
• The transition state wave packet (TSWP) method offers a powerful approach for these calculations.
• Accurate quantum mechanical treatments are essential, especially for tunneling phenomena.

Purpose of the Study:

• To implement and validate the 3D transition state wave packet (TSWP) method within the Heidelberg MCTDH package.
• To compute the cumulative isomerization probability N(E) for the HCN to CNH reaction.
• To assess the efficiency of reduced dimensionality approaches for chemical dynamics.

Main Methods:

• Employed one time-independent and two time-dependent TSWP methods.
• Utilized Chebyshev polynomial expansion for the time-independent approach.
• Applied split operator and multiconfiguration time-dependent Hartree (MCTDH) algorithms for time-dependent propagations.
• Benchmarked calculations on the HCN-->CNH isomerization at zero total angular momentum.

Main Results:

• Successfully implemented the TSWP method in the MCTDH package, marking its first use.
• Obtained accurate 3D calculations of the isomerization probability N(E), providing insights into tunneling.
• Demonstrated the viability of reduced dimensionality approaches by comparing with full 3D results.
• Validated methods for calculating flux operator eigenvectors.

Conclusions:

• The time-dependent TSWP method with MCTDH is suitable for treating more quantum modes in larger systems.
• The developed 3D approach, adapted for Jacobi coordinates, can be applied to H-transfer in larger systems.
• Simplification of the kinetic energy operator is feasible for pseudo triatomic systems.
• The study provides a reliable computational framework for complex chemical dynamics.