A Failure of DFT Is Not Necessarily a DFT Failure-Performance Dependencies on Model System Choices

Area of Science:

• Computational chemistry
• Solid-state chemistry
• Materials science

Background:

• Density Functional Theory (DFT) is widely used for electronic structure calculations.
• Previous studies suggest DFT methods, including DFT with empirical dispersion correction (DFT-D), may not accurately describe weak ruthenium-carbon (Ru-C) interactions.
• A specific claim questioned is that DFT fails to accurately model Ru-C interactions.

Purpose of the Study:

• To re-evaluate the claim regarding DFT's accuracy for weak Ru-C interactions.
• To investigate the reasons for discrepancies between calculated and experimentally determined molecular structures.
• To explore the role of intermolecular forces in crystal structures.

Main Methods:

• Density Functional Theory (DFT) calculations using the BP86 functional.
• DFT with empirical dispersion correction (DFT-D) calculations using the BP86-D2 method.
• Semiempirical lattice energy calculations to model intermolecular forces.

Main Results:

• A mismatch was observed between DFT/DFT-D calculated structures of isolated molecules and X-ray determined crystal structures.
• The study identified that the chemical model system used in calculations was insufficient.
• Intermolecular forces within the crystal's molecular surroundings were identified as a significant factor.

Conclusions:

• The perceived inaccuracy of DFT for weak Ru-C interactions may stem from inadequate modeling of the chemical environment.
• Intermolecular forces, not solely DFT limitations, likely explain the incongruity between computational and experimental results.
• A more comprehensive model incorporating intermolecular interactions is necessary for accurate structural predictions in condensed phases.