Density Functional Calculations Based on the Exponential Ansatz.

Area of Science:

• Quantum Chemistry
• Computational Physics
• Theoretical Chemistry

Background:

• Standard density functional calculations rely on Kohn-Sham orbitals.
• An alternative approach uses the Hartree-Fock wave function as a starting point.

Purpose of the Study:

• To explore the application of a singles-based exponential ansatz to density functional calculations.
• To develop a self-consistent method for calculating electronic properties using a Hartree-Fock reference.

Main Methods:

• Utilizing a singles-based exponential ansatz with a single-reference Hartree-Fock wave function.
• Employing the Kohn-Sham Hamiltonian for self-consistent determination of an auxiliary wave function.
• Incorporating spin-symmetry breaking for size-consistent results.
• Introducing a regularization method to prevent instabilities due to self-interaction.

Main Results:

• Achieved size-consistent results free of unphysical fractional charges at the dissociation limit.
• Demonstrated consistency with standard Kohn-Sham density functional calculations for equilibrium and repulsive geometries.
• Successfully stabilized calculations at moderately long distances using the regularization method.
• Presented a time-dependent extension capable of describing multi-electron excited quantum states.

Conclusions:

• The exponential ansatz provides a viable alternative for density functional calculations, particularly when combined with Hartree-Fock orbitals.
• The developed regularization method enhances the robustness and physical meaningfulness of the approach.
• The time-dependent extension opens possibilities for studying complex electronic excitations.