Well-behaved versus ill-behaved density functionals for single bond dissociation: Separating success from disaster...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Density Functional Theory (DFT) is widely used for electronic structure calculations.
• Unrestricted DFT methods are generally reliable for homolytic bond dissociation in neutral species.
• Delocalization errors are typically minimal in these systems.

Purpose of the Study:

• To investigate the performance of various DFT approximations for the H2 molecule dissociation.
• To identify specific functionals that exhibit failures in describing the dissociation curve.
• To understand the underlying causes of these failures.

Main Methods:

• Unrestricted density functional theory (DFT) calculations.
• Analysis of the H2 molecule dissociation curve.
• Evaluation of static polarizabilities and force constants.

Main Results:

• Several widely used DFT functionals (e.g., B97-D, TPSS) fail to accurately describe H2 dissociation.
• These functionals predict incorrect polarizabilities and force constants.
• Some functionals introduce artificial barriers to H atom association.
• Failures are linked to incomplete spin localization and poor self-consistent density prediction.

Conclusions:

• The performance of DFT functionals varies significantly for H2 dissociation.
• Problematic functionals can lead to unphysical results in electronic structure calculations.
• Caution is advised when using these functionals in ab initio dynamics, especially with electrostatic interactions.