Lewis-based valence bond scheme: application to the allyl cation

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Resonance is a key concept in chemistry, explaining delocalized electrons in molecules.
• Accurate calculation of resonance energy is crucial for understanding molecular stability and reactivity.
• Existing methods like breathing orbital valence bond (BOVB) provide benchmarks for resonance energy calculations.

Purpose of the Study:

• To introduce a novel computational method, valence bond BOND (VBB), for expressing wave functions using Lewis structures.
• To test the efficacy of the VBB method on the allyl cation system.
• To compare VBB results with established methods like BOVB for resonance energy calculations.

Main Methods:

• Development of the valence bond BOND (VBB) computational scheme.
• Application of VBB to model the allyl cation.
• Optimization of sigma orbitals to adapt to individual resonance structures, incorporating the breathing orbital effect.
• Comparison of VBB resonance energy with BOVB results.

Main Results:

• The VBB method provides resonance energy values consistent with BOVB for the allyl cation (54 kcal/mol for VBB vs. 55 kcal/mol for BOVB).
• The optimization of sigma orbitals using the breathing orbital effect enhances the accuracy of the resonance energy calculation.
• A resonance energy of 63 kcal/mol was obtained at the optimized VBB level, indicating the efficiency of the sigma frame's adaptation.

Conclusions:

• The valence bond BOND (VBB) method offers a viable and consistent approach for calculating wave functions using Lewis structures.
• The breathing orbital effect, achieved through sigma orbital optimization, significantly improves the calculation of resonance energy.
• VBB provides accurate and efficient computational results for molecular systems exhibiting resonance, such as the allyl cation.