Semilocal density functional obeying a strongly tightened bound for exchange

Area of Science:

• Physics
• Materials Science
• Chemistry

Background:

• Density functional theory (DFT) is crucial for electronic structure calculations.
• Approximating the exchange-correlation energy is a key challenge in DFT.
• Exact constraints guide the development of accurate DFT functionals.

Purpose of the Study:

• To introduce a new meta-generalized gradient approximation (meta-GGA) for exchange, termed meta-GGA made very simple (MGGA-MVS).
• To develop an exchange functional that satisfies a recently proven optimal bound for exchange energy.
• To evaluate the performance of MGGA-MVS in predicting thermochemical properties and molecular interactions.

Main Methods:

• Developed the meta-GGA made very simple (MGGA-MVS) exchange functional.
• Ensured the MGGA-MVS functional respects the optimal bound on exchange energy.
• Hybridized the nonempirical MGGA-MVS meta-GGA with 25% exact exchange.

Main Results:

• The MGGA-MVS functional satisfies a strong, optimal lower bound on exchange energy, a feat not achieved by previous beyond-local spin-density approximation (LSDA) functionals.
• Despite the tight constraint, MGGA-MVS improved predicted thermochemical properties compared to the Perdew-Burke-Ernzerhof (PBE) GGA.
• The exchange enhancement factor in MVS exhibits a strong dependence on the orbital kinetic energy density.
• Hybridizing MVS with exact exchange yielded excellent predictions for atomization energies, reaction barriers, and weak molecular interactions.

Conclusions:

• The MGGA-MVS meta-GGA represents a significant advancement in DFT, offering improved accuracy through adherence to fundamental constraints.
• The strong dependence on orbital kinetic energy density is key to MVS's success.
• Hybrid global functionals based on MVS show great promise for accurate molecular property predictions.