σ, π aromaticity and anti-aromaticity as retrieved by the linear response kernel

Area of Science:

• Quantum Chemistry
• Theoretical Chemistry
• Computational Chemistry

Background:

• Aromaticity is a key concept in chemistry, influencing molecular properties and reactivity.
• Conceptual Density Functional Theory (DFT) offers tools to probe electronic structure.
• Quantifying aromaticity, especially distinguishing σ and π contributions, remains an active research area.

Purpose of the Study:

• To investigate the chemical importance of the linear response kernel in DFT.
• To assess the linear response kernel's ability to classify and quantify aromaticity and anti-aromaticity.
• To explore the linear response kernel's applicability to σ and π systems, varying ring sizes, and reaction pathways.

Main Methods:

• Utilizing the linear response kernel from conceptual DFT.
• Analyzing σ and π aromatic and anti-aromatic systems.
• Examining molecules of varying ring sizes (five- to eight-membered).
• Investigating transition states of chemical reactions (Diels-Alder, acetylene trimerisation).
• Mathematically proving the correlation with the Para Delocalisation Index (PDI).

Main Results:

• The linear response kernel accurately classifies and quantifies aromaticity for five- to eight-membered systems.
• Splitting the linear response into σ and π contributions provides significant insights.
• The method correctly predicts aromatic transition states and behaves predictably along reaction coordinates.
• A strong correlation between the linear response and PDI is mathematically established.

Conclusions:

• The linear response kernel is a robust DFT index for probing σ and π aromaticity/anti-aromaticity.
• This method is reliable for both equilibrium and non-equilibrium molecular states.
• The findings validate the linear response kernel as a versatile tool in computational chemistry.