Explanation of the Source of Very Large Errors in Many Exchange-Correlation Functionals for Vanadium Dimer

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Vanadium dimer presents a significant challenge for existing Kohn-Sham (KS) density functional theory (DFT) approximations.
• Many exchange-correlation (xc) functionals exhibit substantial errors in predicting the bond energy of vanadium dimer.

Purpose of the Study:

• To evaluate the accuracy of 43 xc functionals and the Hartree-Fock (HF) method for calculating vanadium dimer bond energies.
• To investigate the underlying reasons for large errors in KS-DFT calculations of transition metal compounds.

Main Methods:

• Tested 43 exchange-correlation (xc) functionals and Hartree-Fock (HF) method.
• Analyzed atomic and molecular orbital energies to correlate with bond energy errors.

Main Results:

• KS calculations showed errors ranging from -61.5 to +60.5 kcal/mol, compared to the experimental value of 64.2 kcal/mol.
• The HF method yielded a significantly larger error of -124.4 kcal/mol.
• Errors in bond energy were primarily linked to the calculated energy gap between vanadium atom's 4s and 3dz2 orbitals, particularly the 3dz2 orbital energy.

Conclusions:

• The accuracy of single-particle orbital energies, especially for the 3dz2 orbital, is crucial for predicting transition metal bond energies.
• Improving atomic orbital energy calculations offers a promising pathway to enhance theoretical predictions for metal-containing molecules.
• The nonlocal Hartree-Fock exchange impacts atomic orbital energies, but further research is needed to understand variations among local functionals.