Understanding Electronic Excitations Between Single Determinants with Occupied-Virtual Orbitals for Chemical Valence

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Calculating electronic excited states is crucial for understanding chemical phenomena.
• Current methods often treat ground and excited states as single determinants.
• Analyzing orbital character in these calculations requires refined techniques.

Purpose of the Study:

• To extend the occupied-virtual orbitals for chemical valence (OVOCV) theory for excitation analysis.
• To introduce an intermediate frozen state for cleaner excitation separation.
• To analyze orbital relaxation effects in various electronic excitation calculations.

Main Methods:

• Developed and applied the occupied-virtual orbitals for chemical valence (OVOCV) excitation analysis.
• Utilized orbital-optimized density functional theory (OO-DFT) calculations.
• Introduced a polarization-free intermediate frozen state for analysis.

Main Results:

• OVOCV analysis successfully characterizes excitations, including charge-transfer, core, and valence states.
• Orbital relaxation effects were quantified, showing significant contributions (4-5 eV) in charge-transfer states.
• Demonstrated that direct use of natural transition orbitals (NTOs) can obscure orbital relaxation effects.

Conclusions:

• The extended OVOCV theory provides a robust framework for analyzing electronic excitations.
• Orbital relaxation is a significant factor in excitation energies that needs careful consideration.
• OVOCV analysis offers a more comprehensive understanding of electronic excitations compared to NTO analysis.