Improved constraint satisfaction in a simple generalized gradient approximation exchange functional.

Area of Science:

• Computational chemistry
• Materials science
• Quantum mechanics

Background:

• Generalized gradient approximations (GGAs) are widely used for electronic structure calculations.
• The Perdew-Burke-Ernzerhof (PBE) functional is a common choice, but improvements are sought.
• Previous work introduced a simple GGA exchange functional (Vela-Medel-Trickey or VMT) with improved energetics.

Purpose of the Study:

• To investigate the impact of asymptotic constraints on GGA exchange functionals.
• To develop and evaluate a new GGA exchange functional, VT{8,4}, based on these constraints.
• To assess the performance of VT{8,4} and VMT exchange functionals, particularly when combined with established correlation functionals.

Main Methods:

• Development of a new GGA exchange functional (VT{8,4}) by imposing an asymptotic constraint at large electron density gradients.
• Combination of the new VT{8,4} and existing VMT exchange functionals with the Lee-Yang-Parr (LYP) correlation functional.
• Extensive computational testing of the functionals on various datasets to evaluate their accuracy in predicting energetics.

Main Results:

• The VT{8,4} functional, with the imposed large-s constraint, shows modest further improvement over the VMT functional.
• Combining VT{8,4} or VMT exchange with LYP correlation yields additional performance gains.
• The proposed functionals demonstrate improved energetics compared to standard PBE, while maintaining simplicity.

Conclusions:

• Asymptotic constraints play a role in refining GGA exchange functionals.
• The VT{8,4} functional represents a viable and slightly improved alternative to VMT.
• The combination of these refined exchange functionals with LYP correlation offers a promising route for accurate electronic structure calculations.