Magnetic Coupling in Non-Kekulé Diradical Hydrocarbons via Multiconfigurational Pair-Density Functional Theory

Area of Science:

• Quantum computing and nanotechnology
• Materials science and condensed matter physics

Background:

• Studying electron spins in nanomaterials is vital for quantum technologies but faces experimental and theoretical hurdles.
• Radicals' instability and computationally intensive quantum mechanical methods limit nanoscale spin process understanding.
• Nanographenes with diradical character exhibit unique magnetic and electric properties.

Purpose of the Study:

• To investigate magnetic coupling in non-Kekulé diradicals and nanographene models.
• To address the limitations of standard density functional theory in describing certain molecular ground states.
• To introduce and validate a computationally efficient quantum mechanical method.

Main Methods:

• Utilized a recently developed (range-separated) multiconfigurational on-top pair density functional theory (MC-sr-ctPDFT) method.
• Studied magnetic coupling in small model non-Kekulé diradicals and nanographene models.
• Compared the new method's accuracy and computational cost against established methods like NEVPT2 and CASPT2.

Main Results:

• Demonstrated that standard density functional theory incorrectly describes molecules with singlet ground states, sometimes violating Hund's rule.
• The MC-sr-ctPDFT method accurately captures both static and dynamic electron correlations.
• MC-sr-ctPDFT shows comparable accuracy to NEVPT2 and CASPT2 but with significantly lower computational cost.

Conclusions:

• The developed MC-sr-ctPDFT method offers a computationally efficient and accurate alternative for studying spin phenomena in nanomaterials.
• This method overcomes key limitations of existing theoretical approaches for complex spin systems.
• Future applications could include investigating surface interactions and catalytic processes in complex molecular environments.