Excited State Dipole Moments in Solution: Comparison between State-Specific and Linear-Response TD-DFT Values

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Continuum solvation models are essential for understanding solvent effects on molecular properties.
• Time-dependent density functional theory (TD-DFT) is a common method for studying excited electronic states.
• Previous work highlighted the importance of state-specific (SS) models for excited-state energy calculations.

Purpose of the Study:

• To compare linear-response (LR) and state-specific (SS) formalisms for coupling solvation models with TD-DFT.
• To investigate solvent effects on excited state dipole moments of solvated molecules.
• To assess the impact of different response schemes on localized and charge-transfer electronic excitations.

Main Methods:

• Coupling of continuum solvation models with TD-DFT.
• Comparison of linear-response (LR) and state-specific (SS) formalisms.
• Analysis of 20 low-lying electronic excitations with varying characters (localized and charge-transfer).

Main Results:

• SS models are important for predicting excited state properties, not just energies.
• LR and SS schemes yield similar dipole moments for local transitions with range-separated functionals.
• Significant differences (a few Debye units) in dipole moments are observed for charge-transfer transitions between LR and SS schemes.

Conclusions:

• The choice of response scheme (LR vs. SS) significantly impacts the prediction of excited state dipole moments, particularly for charge-transfer states.
• An inadequate exchange-correlation functional within the SS framework can lead to substantial overestimation of dipole moments.
• Accurate prediction of solvent effects on excited states requires careful consideration of both the response scheme and the functional used.