Source Function applied to experimental densities reveals subtle electron-delocalization effects and appraises their...

Area of Science:

• Quantum Chemistry
• Chemical Physics
• Crystallography

Background:

• The Source Function (SF) provides insights into chemical bonding by analyzing electron density contributions.
• Understanding local chemical behavior requires considering the influence of the entire molecular system.
• Comparing ab initio and experimental electron density properties necessitates a common, rigorous basis.

Purpose of the Study:

• To review the Source Function (SF) and illustrate its applications in analyzing chemical bonding.
• To explore the SF's capability in detecting and quantifying electron delocalization effects and their transferability.
• To compare SF patterns derived from experimental X-ray diffraction data with ab initio calculations.

Main Methods:

• Application of the Source Function (SF) to in vacuo and crystal systems.
• Analysis of experimentally derived SF patterns from X-ray diffraction data of benzene, naphthalene, and BAB molecular crystals.
• Comparison of SF patterns with ab initio periodic calculations and promolecular densities.

Main Results:

• The SF tool accurately reproduces π-electron conjugation patterns in benzene and naphthalene, showing quantitative agreement with ab initio calculations.
• Chemical substitution effects on electron delocalization transferability were quantified in BAB molecular crystals.
• Promolecular densities failed to reproduce SF trends related to increasing electron delocalization, unlike proper quantum mechanical densities.

Conclusions:

• The Source Function is a powerful tool for discussing chemical bonding and electron delocalization in diverse chemical systems.
• SF analysis enables rigorous comparison between theoretical and experimental electron density properties.
• The study highlights the importance of using accurate quantum mechanical densities for reliable SF pattern analysis.