Local Hartree-Fock orbitals using a three-level optimization strategy for the energy

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Determining localized molecular orbitals is crucial for understanding chemical bonding and electronic structure.
• Traditional methods for orbital localization can be computationally intensive.

Purpose of the Study:

• To develop a more efficient procedure for determining localized Hartree-Fock orbitals.
• To investigate the impact of different starting guesses on the localization process.

Main Methods:

• A three-level energy optimization procedure combined with a refined least-change strategy for orbitals.
• Explicit localization performed at the valence basis level.
• Introduction of a core-valence separation for the least-change occupied orbital space.

Main Results:

• Localized occupied orbitals determined with a small computational cost when using valence basis localized orbitals as a starting guess.
• Approximately half the number of iterations required for unoccupied space localization compared to canonical Hartree-Fock orbitals.
• Different starting guesses may lead to different local minima, but all correspond to orbitals with similar locality.

Conclusions:

• The proposed method significantly enhances the efficiency of determining localized Hartree-Fock orbitals.
• Using valence basis localized orbitals as starting guesses is a computationally advantageous strategy.
• The approach provides a robust way to obtain localized orbitals with consistent locality characteristics.