A Density Functional Valence Bond Study on the Excited States

Area of Science:

• Computational chemistry
• Theoretical chemistry
• Quantum chemistry

Background:

• Accurate description of excited states is vital for electronic structure theory.
• Strong correlation effects and state interactions occur in degenerate or near-degenerate electronic states.
• Multi-state treatments are often necessary for these complex systems.

Purpose of the Study:

• To explore low-lying excited states of isoelectronic systems (C2H, CN, CO+, BO).
• To compare the performance of valence bond self-consistent field (VBSCF) and Hamiltonian matrix correction-based density functional valence bond (hc-DFVB) methods.
• To demonstrate the effectiveness of hc-DFVB in handling strong correlation and state interactions.

Main Methods:

• Application of valence bond self-consistent field (VBSCF) method.
• Utilizing the Hamiltonian matrix correction-based density functional valence bond (hc-DFVB) method, a multi-reference density functional theory approach.
• Analysis of potential energy curves for LiF and a mixed-valence spiro cation.

Main Results:

• hc-DFVB provides significantly improved excitation energies compared to VBSCF.
• hc-DFVB reliably predicts the correct ordering of excited states, resolving VBSCF inconsistencies.
• Key structural contributions and bonding pictures were extracted by categorizing VB structures based on point group symmetry.

Conclusions:

• The hc-DFVB method offers superior accuracy for describing electronic excited states and their interactions.
• hc-DFVB is particularly effective for studying near-degenerate excited states in avoided crossing regions.
• The study highlights the capability of hc-DFVB in advancing electronic structure theory for complex molecular systems.