title: Semilocal density functional obeying a strongly tightened bound for exchange.
abstract: Because of its useful accuracy and efficiency, density functional theory (DFT) is one of the most widely used electronic structure theories in physics, materials science, and chemistry. Only the exchange-correlation energy is unknown, and needs to be approximated in practice. Exact constraints provide useful information about this functional. The local spin-density approximation (LSDA) was the first constraint-based density functional. The Lieb-Oxford lower bound on the exchange-correlation energy for any density is another constraint that plays an important role in the development of generalized gradient approximations (GGAs) and meta-GGAs. Recently, a strongly and optimally tightened lower bound on the exchange energy was proved for one- and two-electron densities, and conjectured for all densities. In this article, we present a realistic "meta-GGA made very simple" (MGGA-MVS) for exchange that respects this optimal bound, which no previous beyond-LSDA approximation satisfies. This constraint might have been expected to worsen predicted thermochemical properties, but in fact they are improved over those of the Perdew-Burke-Ernzerhof GGA, which has nearly the same correlation part. MVS exchange is however radically different from that of other GGAs and meta-GGAs. Its exchange enhancement factor has a very strong dependence upon the orbital kinetic energy density, which permits accurate energies even with the drastically tightened bound. When this nonempirical MVS meta-GGA is hybridized with 25% of exact exchange, the resulting global hybrid gives excellent predictions for atomization energies, reaction barriers, and weak interactions of molecules.
authors.affiliation: Departments of Physics and.
authors.forename: Jianwei
authors.initials: J
authors.lastname: Sun
authors.affiliation: Departments of Physics and Chemistry, Temple University, Philadelphia, PA 19122 perdew@temple.edu.
authors.forename: John P
authors.initials: JP
authors.lastname: Perdew
authors.affiliation: Departments of Physics and.
authors.forename: Adrienn
authors.initials: A
authors.lastname: Ruzsinszky
keywords: density functional theory; exchange energy; lower bound