Exact and exclusive electron localization indices within QTAIM atomic basins.

Area of Science:

• Quantum Chemistry
• Chemical Physics
• Computational Chemistry

Background:

• Traditional localization indices (LIs) within Quantum Theory of Atoms in Molecules (QTAIM) present challenges in interpretation.
• Existing LIs may not accurately represent electron delocalization, potentially leading to misleading chemical and physical interpretations.

Purpose of the Study:

• To introduce novel, exclusive, and easily visualizable measures of electron delocalization within QTAIM.
• To address the limitations of orthodox LIs by proposing a new framework based on density decomposition.

Main Methods:

• Development of new localization indices (LIs) and delocalization indices (DIs) using the Fragment, Atomic, Localized, Delocalized, and Interatomic (FALDI) density decomposition technique.
• Accounting for overlap between localized and delocalized density functions in the new indices.

Main Results:

• The novel FALDI-based LIs and DIs provide exclusive measures of electron delocalization.
• These new indices accurately recover chemically expected core and bonded electron counts.
• 3D representations of the new (de)localization indices offer valuable visualization tools.

Conclusions:

• The proposed FALDI-based electron delocalization indices offer a more accurate and interpretable alternative to traditional QTAIM LIs.
• These new measures provide a valuable bridge between classical conceptual chemistry and quantum chemical topology.
• Demonstrated utility in examples like formamide and benzene highlights the practical applicability of the new indices.