Excited state dipole moments from ΔSCF: a benchmark

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Spectroscopy

Background:

• Molecular electric dipole moments indicate charge distribution and influence molecular response to external electric fields.
• Differences in dipole moments between electronic states allow tuning of photophysics and photochemistry via external electric fields.
• Excited-state properties are crucial for understanding molecular behavior under irradiation.

Purpose of the Study:

• To benchmark the accuracy of excited-state dipole moments calculated using Δ-Self-Consistent Field (ΔSCF) methods.
• To compare ΔSCF results with Time-Dependent Density Functional Theory (TDDFT) and wavefunction-based methods.
• To assess the applicability of ΔSCF for challenging excited states like doubly excited and charge-transfer states.

Main Methods:

• Utilized Δ-Self-Consistent Field (ΔSCF) calculations to determine excited-state dipole moments.
• Compared ΔSCF results against established TDDFT and wavefunction-based computational methods.
• Validated findings against existing literature data for excited-state properties.

Main Results:

• ΔSCF methods provide excited-state dipole moments with accuracy comparable to TDDFT on average.
• ΔSCF shows increased accuracy for certain pathological cases, particularly doubly excited states inaccessible to conventional TDDFT.
• Charge-transfer states calculated with ΔSCF can be more severely affected by DFT overdelocalization error than TDDFT, though beneficial error cancellation occurs in push-pull systems.

Conclusions:

• ΔSCF methods offer a valuable approach for calculating excited-state dipole moments, especially for states challenging for TDDFT.
• The accuracy of ΔSCF is case-dependent, with notable success for doubly excited states.
• Careful consideration of DFT overdelocalization errors is necessary when applying ΔSCF to charge-transfer states.