Beyond Born-Oppenheimer Constructed Diabatic Potential Energy Surfaces for H₃: Adiabatic and Diabatic Reaction...

Area of Science:

• Quantum Chemistry
• Theoretical Chemistry
• Chemical Physics

Background:

• Accurate potential energy surfaces (PESs) are essential for understanding chemical reactions.
• Nonadiabatic effects, arising from the coupling between electronic states, are significant in systems like H3.
• Existing PESs may not adequately capture the complexities of multistate interactions.

Purpose of the Study:

• To construct a global, multistate diabatic Potential Energy Surface (PES) matrix for the H3 system.
• To incorporate first-principles-based Beyond Born-Oppenheimer (BO) theory for enhanced accuracy.
• To provide a PES suitable for precise scattering calculations.

Main Methods:

• Employed ab initio calculations using CASSCF followed by MRCI methods.
• Calculated adiabatic PESs and Nonadiabatic Coupling Terms (NACTs) for the lowest three electronic states (1²A', 2²A', 3²A').
• Located conical intersections by integrating NACTs and solved adiabatic-to-diabatic (ADT) transformation equations.

Main Results:

• Successfully constructed a smooth, single-valued, continuous, and symmetric diabatic PES matrix for the H3 system.
• The PES incorporates accurate ab initio data and accounts for nonadiabatic couplings.
• The developed PES is validated for its suitability in scattering calculations.

Conclusions:

• The constructed diabatic PES matrix provides a robust theoretical framework for H3 system dynamics.
• The Beyond Born-Oppenheimer approach significantly improves the accuracy of the PES.
• This work enables more reliable simulations of scattering processes involving the H3 system.