Dispersion XDM with Hybrid Functionals: Delocalization Error and Halogen Bonding in Molecular Crystals

Area of Science:

• Computational chemistry
• Solid-state physics
• Materials science

Background:

• Accurate relative lattice energies are vital for polymorph ranking and crystal structure prediction.
• Delocalization error in density functional theory (DFT) can impact calculated intermolecular binding and lattice energies.

Purpose of the Study:

• To explore dispersion-corrected hybrid functionals within the planewave-pseudopotentials approach to mitigate delocalization error.
• To assess the performance of these functionals in calculating gas-phase binding and molecular crystal lattice energies.

Main Methods:

• Combining hybrid functionals with the exchange-hole dipole moment (XDM) model for dispersion correction.
• Utilizing the planewave-pseudopotentials approach for calculations.
• Applying a method to calculate Bader's delocalization indices to quantify intermolecular delocalization.

Main Results:

• XDM-corrected hybrid functionals generally outperform GGA functionals for binding and lattice energies.
• Hybrid functionals accurately predict lattice energies for halogen-bonded crystals (Cl2, Br2, I2, ICl), unlike GGA functionals which overestimate them.
• Intermolecular delocalization indices effectively measure halogen bond strength and detect delocalization error.

Conclusions:

• Dispersion-corrected hybrid functionals offer a robust solution to delocalization error in molecular crystal energy calculations.
• The study provides a reliable method for accurate crystal structure prediction and polymorph ranking.
• Delocalization indices serve as valuable metrics for understanding intermolecular interactions in crystals.