A detailed comparison of ΔSCF methods with the constraint-based orbital-optimized excited state method

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Linear-response theories have limitations for determining electronically excited states.
• Orbital-optimized methods are gaining popularity for variational excited state calculations.
• Established ΔSCF methods have known shortcomings in accuracy and stability.

Purpose of the Study:

• To compare established ΔSCF methods with the constraint-based orbital-optimized excited states (COOX) method.
• To introduce and analyze a ΔCOOX method based on specific orbital rotations.
• To evaluate the accuracy and stability of COOX and ΔCOOX for various excitation types.

Main Methods:

• Application of the constraint-based orbital-optimized excited states (COOX) method.
• Development and application of a ΔCOOX method by adapting COOX to ΔSCF orbital rotations.
• Calculations performed on diverse molecular systems for valence, core, Rydberg, double, and charge-transfer excitations.

Main Results:

• The COOX approach demonstrates superior stability compared to established ΔSCF methods.
• Both COOX and ΔCOOX yield results of comparable quality across various excitation types.
• Detailed analysis of differences in performance, accuracy, and stability between the methods.

Conclusions:

• The COOX method is a more stable and reliable approach for variational excited state calculations.
• COOX offers significant advantages over ΔSCF, particularly in computational stability.
• The proposed ΔCOOX method provides a valuable tool for analyzing orbital-optimized excited state calculations.