On the interpretation of valence bond wavefunctions

Area of Science:

• Quantum Chemistry
• Theoretical Chemistry

Background:

• Valence bond (VB) theory provides a framework for understanding chemical bonds, aligning with chemists' intuitive models.
• VB structures can represent different bonding scenarios, including covalent bonds (equal electron distribution) and ionic bonds (charge separation).

Purpose of the Study:

• To explore how the weights of individual structures in a multi-structure VB wavefunction can quantify different bonding types.
• To investigate the physical interpretation of individual VB structures for diatomic and polyatomic molecules.
• To examine the relationship between VB structures and classical Lewis structures.

Main Methods:

• Utilizing variationally optimized multi-structure valence bond wavefunctions.
• Analyzing the contribution (weights) of individual VB structures to the overall wavefunction.
• Applying the methodology to simple diatomic and polyatomic molecules.

Main Results:

• The weights of VB structures in optimized wavefunctions directly correlate with the degree of covalent and ionic character.
• Individual VB structures can be interpreted as representing distinct physical bonding situations.
• The study highlights inconsistencies arising from assuming independent physical properties for each VB structure.

Conclusions:

• Multi-structure VB wavefunctions offer a quantitative method to assess the importance of various bonding types.
• Interpreting individual VB structures as distinct physical entities is a useful concept but requires careful consideration of their interdependence.
• The assumption of isolated properties for individual VB structures is not universally valid and can lead to theoretical contradictions.