Communication: orbital instabilities and triplet states from time-dependent density functional theory and long-range...

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Long-range corrected (LRC) hybrid functionals are widely used in density functional theory (DFT) for chemical applications.
• These functionals have shown success in describing various electronic properties.

Purpose of the Study:

• To evaluate the performance of LRC hybrid functionals for time-dependent DFT (TDDFT) calculations of triplet excited states.
• To identify potential issues and limitations of these functionals in describing triplet states.

Main Methods:

• Utilized TDDFT framework to investigate triplet excited states.
• Employed various LRC hybrid functionals with different range-separation parameters.
• Analyzed the sensitivity of triplet energies to the range-separation parameter.

Main Results:

• Triplet energies calculated using LRC functionals are highly sensitive to the range-separation parameter.
• This sensitivity arises from ground-state triplet instabilities inherent in these functionals.
• Large amounts of Hartree-Fock exchange in LRC functionals contribute to these instabilities.

Conclusions:

• Standard LRC hybrid functionals are not recommended for TDDFT descriptions of triplet excited states.
• Careful consideration of functional choice and parameterization is needed for accurate triplet state calculations.
• Further development of DFT functionals may be required for reliable triplet state predictions.