Dynamic-then-Static Approach for Core Excitations of Open-Shell Molecules

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Delta self-consistent-field (Delta SCF) methods are standard for studying electronically excited states.
• A key limitation is spin contamination in nonaufbau determinants, affecting accuracy.
• Accurate treatment of spin-coupling interactions in open-shell systems remains a challenge.

Purpose of the Study:

• To develop a general and accurate method for spin-coupling interactions in open-shell molecules.
• To address spin contamination issues inherent in traditional Delta SCF methods.
• To provide a computationally efficient yet accurate approach for excited state calculations.

Main Methods:

• Utilized multistate density functional theory (MSDFT) to model spin-coupling.
• Obtained effective exchange integrals by enforcing multiplet degeneracy.
• Ensured consistency with high-spin state energies treated by Kohn-Sham density functional theory (DFT).

Main Results:

• The MSDFT approach effectively resolves spin contamination in open-shell molecules.
• Calculations on core excitations showed excellent agreement with experimental data.
• The BLYP functional with the aug-cc-pCVQZ basis set yielded highly accurate results.

Conclusions:

• MSDFT offers a robust solution for spin-coupling in open-shell systems.
• This method combines the efficiency of DFT with the accuracy of wave function theory.
• MSDFT is a promising tool for accurate and efficient computational studies of excited states.