Convex Hartree-Fock theory for modeling ground state conical intersections.

Area of Science:

• Computational Chemistry
• Theoretical Chemistry
• Molecular Dynamics

Background:

• Accurate modeling of conical intersections is vital for understanding nonadiabatic molecular dynamics, including radiationless transitions and photochemical reactions.
• Conventional electronic structure methods (Hartree-Fock, DFT, TD-DFT) struggle with conical intersections due to their single-reference nature.
• Multiconfigurational methods can capture these features but are computationally expensive.

Purpose of the Study:

• To develop a computationally efficient method for accurately modeling conical intersections.
• To introduce a modified Hartree-Fock framework, Convex Hartree-Fock (CHF), as an alternative to existing methods.

Main Methods:

• Proposing Convex Hartree-Fock (CHF), a modified Hartree-Fock approach.
• Optimizing the reference within a tailored subspace by removing projections along selected Hessian eigenvectors.
• Obtaining ground and excited states via subsequent Hamiltonian diagonalization.

Main Results:

• The CHF method was validated across several test cases.
• Performance was benchmarked against time-dependent Hartree-Fock within the Tamm-Dancoff approximation.

Conclusions:

• Convex Hartree-Fock provides a promising approach for accurate and computationally feasible modeling of conical intersections.
• This method addresses limitations of conventional electronic structure theories in nonadiabatic molecular dynamics.