Good Vibrations: Calculating Excited-State Frequencies Using Ground-State Self-Consistent Field Models.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Excited electronic states are crucial for understanding photochemistry and spectroscopy.
• Traditional methods like CIS and TD-DFT for excited states can be computationally expensive.
• Delta-self-consistent field (Δ-SCF) approaches offer a potential alternative for studying these states.

Purpose of the Study:

• To evaluate the efficacy of Δ-SCF methods for calculating excited-state vibrational frequencies.
• To compare Δ-SCF results with established methods such as CIS and TD-DFT.
• To investigate the impact of spin contamination and the utility of spin purification models.

Main Methods:

• Calculations of excited-state vibrational frequencies using Δ-SCF.
• Comparison of Δ-SCF results with Configuration Interaction with Single substitutions (CIS) and Time-Dependent Density Functional Theory (TD-DFT).
• Application of an approximate spin purification model for spin-contaminated excited-state SCF solutions.

Main Results:

• Δ-SCF calculations provide accurate excited-state vibrational frequencies for representative molecules.
• The performance of Δ-SCF is comparable to CIS and TD-DFT methods.
• Spin purification can improve results when excited-state SCF solutions exhibit spin contamination.

Conclusions:

• Δ-SCF provides an accurate and cost-effective method for determining excited-state vibrational frequencies.
• This SCF-based approach serves as a valuable alternative to CIS and TD-DFT for excited-state potential energy surface calculations.
• The findings highlight the potential of Δ-SCF in advancing the study of excited-state dynamics and properties.