Analytic Route to Tunneling Splittings Using Semiclassical Perturbation Theory

Area of Science:

• Quantum chemistry
• Theoretical chemistry
• Chemical physics

Background:

• Tunneling splittings are crucial for understanding reaction dynamics in multidimensional systems.
• Accurate calculation of tunneling splittings often requires computationally expensive methods.
• Existing methods may not fully account for anharmonicity and corner-cutting effects.

Purpose of the Study:

• To present an efficient, analytical, and simple computational route for approximating tunneling splittings.
• To enable direct calculation from ab initio data without a full potential energy surface.
• To provide a reliable tool for studying chemical dynamics.

Main Methods:

• Combines the Wentzel-Kramers-Brillouin (WKB) approximation with vibrational perturbation theory.
• Implicitly accounts for anharmonicity and corner-cutting effects.
• Utilizes direct ab initio computations.

Main Results:

• The method provides accurate approximations for tunneling splittings.
• Demonstrated efficiency and reliability on model and real chemical systems.
• Successfully applied to malonaldehyde and tropolone isomerization.

Conclusions:

• The developed method offers an efficient and reliable approach to approximate tunneling splittings.
• Simplifies the study of tunneling phenomena in multidimensional chemical systems.
• Facilitates direct application using ab initio data.