Overcoming low orbital overlap and triplet instability problems in TDDFT

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Time-dependent density functional theory (TDDFT) faces challenges with low orbital overlap and triplet instability.
• Accurate calculation of excitation energies, especially triplet states, is crucial in quantum chemistry.

Purpose of the Study:

• To investigate and resolve low orbital overlap and triplet instability issues in TDDFT.
• To evaluate a new benchmark set for singlet and triplet excitation energies.
• To assess the performance of Coulomb-attenuated functionals and the Tamm-Dancoff approximation.

Main Methods:

• Utilized a new benchmark set of challenging singlet and triplet excitation energies.
• Employed Coulomb-attenuated functionals to address low orbital overlap.
• Applied the Tamm-Dancoff approximation to mitigate triplet instability errors.

Main Results:

• Coulomb-attenuated functionals largely overcome low orbital overlap issues for singlet and triplet states.
• Triplet instability problems persist for high overlap excitations across various functionals.
• The Tamm-Dancoff approximation reduces errors for high overlap excitations without affecting low overlap ones.

Conclusions:

• A synergy exists between orbital overlap and stability in TDDFT calculations.
• The combined Coulomb-attenuated Tamm-Dancoff approach demonstrates success in improving excitation energy calculations.
• This method offers a robust solution for challenging electronic excitation problems.