Symmetric Group Semiempirical Valence Bond Method for Large Conjugated Molecules

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Valence Bond (VB) theory is crucial for understanding molecular electronic structure.
• Handling large molecular systems with traditional VB methods is computationally intensive.
• Accurate prediction of electronic properties requires efficient theoretical models.

Purpose of the Study:

• To introduce a novel and efficient computational method, the symmetric group semiempirical valence bond (SGSVB) method.
• To enable the study of large molecular systems using Valence Bond theory.
• To accurately calculate vertical excitation energies and electronic structures.

Main Methods:

• Developed the SGSVB method based on symmetric group representations.
• Utilized bonded tableau functions for direct VB wave function construction.
• Employed truncation of overlap integrals for efficient matrix element calculation.
• Assumed orbital orthogonality for two-electron energy computations.

Main Results:

• SGSVB accurately predicted vertical excitation energies for linear polyenes, showing good agreement with experimental data.
• Extrapolation to infinite chain length for polyenes yielded limiting energies consistent with literature.
• Investigated circumcoronene, obtaining Kekulé structure weights highly correlated with wave function-based resonance theory (WFRT) results.

Conclusions:

• The SGSVB method provides a novel and efficient computational tool for Valence Bond theory.
• SGSVB is effective for elucidating the π-electron structure of complex molecular systems.
• The method demonstrates significant potential for future applications in computational chemistry.