Orbitals with intermediate localization and low coupling: spanning the gap between canonical and localized orbitals

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Electronic Structure Theory

Background:

• Canonical orbitals offer delocalized representations of electronic structure.
• Existing localization techniques often lead to over-localization, reducing interpretability and creating nonintuitive orbital interactions.
• Strong interorbital coupling and unmeaningful diagonal Fock energies are drawbacks of current over-localization methods.

Purpose of the Study:

• To develop a novel method for generating orbitals of intermediate localization.
• To bridge the gap between fully delocalized (canonical) and fully localized orbitals.
• To enhance the interpretability of electronic structure while preserving accurate orbital energies.

Main Methods:

• Introduction of a new procedure to create orbitals with intermediate localization.
• Development of techniques to control the degree of localization and interorbital coupling.
• Application to conjugated π systems and molecular fragments.

Main Results:

• Generated orbitals of intermediate localization that balance locality and interpretability.
• Preserved the diagonal nature of the Fock matrix to a specified error tolerance.
• Successfully localized π spaces into weakly coupled units in molecular fragment systems.
• Maintained expected structure for highly coupled orbitals as weakly coupled orbitals separated.

Conclusions:

• The developed method provides orbitals that are more chemically intuitive than fully localized ones.
• Intermediate localization orbitals maintain accurate orbital energies, unlike some existing methods.
• This technique offers a unique approach to orbital localization, improving upon current limitations.