Mixed-Reference Spin-Flip Time-Dependent Density Functional Theory (MRSF-TDDFT) as a Simple yet Accurate Method for...

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Diradicals and diradicaloids possess multiconfigurational electronic states due to strong electron correlation.
• Accurate quantum chemical description of these systems is computationally challenging.
• Conventional density functional theory (DFT) methods often struggle with spin-contamination and accuracy for diradicals.

Purpose of the Study:

• To evaluate the accuracy of the mixed-reference spin-flip time-dependent density functional theory (MRSF-TDDFT) method for diradicals and diradicaloids.
• To investigate the adiabatic singlet-triplet (ST) gaps in various diradical systems using MRSF-TDDFT.
• To propose a criterion for distinguishing diradicals and diradicaloids.

Main Methods:

• Application of the mixed-reference spin-flip time-dependent density functional theory (MRSF-TDDFT) method.
• Study of adiabatic singlet-triplet (ST) gaps in a series of diradicals and diradicaloids.
• Analysis of specific phenomena like Jahn-Teller distortion and Hund's rule violation.

Main Results:

• MRSF-TDDFT demonstrates high prediction accuracy for adiabatic ST gaps, with a mean absolute error (MAE) of 0.14 eV.
• The method accurately describes complex electronic effects, including Jahn-Teller distortion and Hund's rule violation in specific diradicals.
• MRSF-TDDFT results are consistent with experimental data and high-level ab initio computations, outperforming conventional DFT methods.

Conclusions:

• MRSF-TDDFT is a reliable and accurate method for studying the electronic structure of diradicals and diradicaloids.
• The study validates the utility of MRSF-TDDFT for systems with strong electron correlation.
• Guidelines for applying MRSF-TDDFT to challenging molecular systems are provided.