Electron Localization Function at the Correlated Level: A Natural Orbital Formulation.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Materials Science

Background:

• The electron localization function (ELF) is crucial for understanding chemical bonding.
• Calculating ELF typically requires two-particle density (2-PD), limiting its use with certain computational methods.
• Correlated methods like CCSD and MP2 are powerful but often incompatible with standard ELF calculations due to 2-PD requirements.

Purpose of the Study:

• To develop a computationally efficient approximation for the electron localization function (ELF).
• To enable the calculation of ELF using correlated methods that do not readily provide two-particle density (2-PD).
• To facilitate routine ELF analysis in medium-sized molecules.

Main Methods:

• A 2-fold approximation strategy was developed for ELF calculation.
• The first approximation refines the ELF computation itself.
• The second approximation estimates pair populations within ELF basins, utilizing natural orbitals and their occupancies.

Main Results:

• The proposed method successfully calculates ELF without explicit two-particle density (2-PD).
• Natural orbitals and their occupancies, readily available from most electronic structure methods, are sufficient inputs.
• The approximation allows the use of advanced correlated methods (e.g., CCSD, MP2) for ELF analysis.

Conclusions:

• This work presents a practical and robust approximation for ELF calculations.
• The method overcomes limitations associated with two-particle density (2-PD) in correlated electronic structure theory.
• It paves the way for routine ELF analysis in medium-sized molecules using high-level computational chemistry techniques.