Molecular spin on surface: From strong correlation to dispersion interactions.

Area of Science:

• Computational materials science
• Quantum chemistry
• Surface science

Background:

• Predicting magnetic properties of surface-supported molecules is crucial but challenging for electronic structure theory.
• Strong electron correlation and molecule-surface dispersion interactions significantly impact these properties.

Purpose of the Study:

• To develop and validate a reliable computational method for predicting magnetic properties of surface-supported molecules.
• To investigate the role of strong correlation and dispersion interactions in determining spin state energetics.

Main Methods:

• Utilizing Hubbard-U corrected van der Waals density functional (vdW-DF) theory.
• Fitting the optimal U value for Fe(ii) compounds to determine spin state energetics.
• Employing Cu(111)-supported metallocenes (Fe, Co) as a prototype system to study molecule-surface interactions.

Main Results:

• The optimal U value for vdW-DF is smaller than LDA but similar to GGA.
• vdW-DF+U overestimates bond distances but yields ΔEHL consistent with LDA+U and experiments.
• Non-local dispersion interactions captured by vdW-DF are critical for ΔEHL at larger molecule-surface distances.
• Molecule-metal contact weakens the ligand field and decreases ΔEHL.

Conclusions:

• Hubbard-U corrected vdW-DF provides an accurate approach for predicting magnetic properties of surface-supported molecules.
• Dispersion interactions and molecule-surface contact significantly influence spin state energetics.