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A Local Diabatisation Method for Two-State Adiabatic Conical Intersections
Eva Vandaele1, Momir Mališ1, Sandra Luber1
1Department of Chemistry, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland.
Journal of Chemical Theory and Computation
|January 4, 2024
Summary
This study introduces a new method to analyze conical intersections (CIs) using electronic structure calculations. The approach enables the calculation of nonadiabatic coupling vectors without wave functions, crucial for understanding molecular dynamics.
Area of Science:
- Quantum Chemistry
- Theoretical Chemistry
- Computational Chemistry
Background:
- Conical intersections (CIs) are critical points in molecular electronic structure where adiabatic states become degenerate.
- Characterizing CIs is essential for understanding nonadiabatic processes, such as internal conversion and photochemical reactions.
- Existing methods for calculating nonadiabatic coupling (NAC) vectors often require wave functions, limiting their applicability.
Purpose of the Study:
- To develop a novel, wave-function-free methodology for the local characterization of conical intersections.
- To enable the calculation of nonadiabatic coupling vectors based on energy gradients and Hessians at the CI.
- To demonstrate the broad applicability of the new method across various molecular systems and computational levels.
Main Methods:
- The methodology identifies branching space coordinates from the Hessian and gradient at the CI.
- Potential energy surfaces near the CI are expressed in a diabatic representation.
- Nonadiabatic coupling vectors are computed using an energy-based, wave-function-free approach.
Main Results:
- The method was successfully applied to investigate minimum-energy CIs (MECIs) in formamide (S1-S2) using SA-CASSCF and XMS-CASPT2.
- Asymmetrical MECIs in cyclopropanone (S0-S1) were analyzed using SA-CASSCF.
- CIs in benzene (S1-S2) and thiophene (S1-S2) were studied using SA-CASSCF, TDDFT, and XMS-CASPT2, showcasing the method's versatility.
Conclusions:
- The developed methodology provides a robust and versatile tool for characterizing conical intersections.
- This wave-function-free approach simplifies the calculation of NAC vectors, expanding their accessibility in theoretical chemistry.
- The successful application to diverse systems highlights the method's potential for advancing the study of nonadiabatic molecular dynamics.
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