Orthogonally Constrained Orbital Optimization: Assessing Changes of Optimal Orbitals for Orthogonal Multireference...

Area of Science:

• Quantum Chemistry
• Computational Physics
• Electronic Structure Theory

Background:

• Configuration interaction (CI) calculations are crucial for understanding molecular electronic states.
• The selection of molecular orbitals significantly impacts the accuracy of CI results.
• Existing methods may struggle to accurately represent both ground and excited states simultaneously.

Purpose of the Study:

• To develop a novel method for generating state-specific orbitals in configuration interaction calculations.
• To improve the accuracy of excitation energy calculations.
• To reduce the computational cost associated with large configuration interaction expansions.

Main Methods:

• Employed an orthogonally constrained orbital optimization technique.
• Developed a democratic description for ground and excited states.
• Generated state-specific orbitals tailored to individual electronic states.

Main Results:

• The proposed method accurately reproduced the excitation energy for a four-electron Hubbard trimer.
• State-average calculations showed significant deviations (up to a factor of 2.5) in excitation energy.
• Demonstrated the effectiveness of state-specific orbitals in achieving spectroscopic accuracy.

Conclusions:

• Orbital optimization is essential for accurate configuration interaction calculations.
• State-specific orbitals offer a significant advantage over state-average approaches for excited state properties.
• The developed method provides a pathway to more reliable and efficient electronic structure calculations.