PBEsol

PBEsol, short for PBE for solids, is a density functional within the generalized gradient approximation (GGA) family used in density functional theory. It is a revised version of the PBE functional optimized specifically for solids and their surfaces, with the aim of improving equilibrium properties such as lattice constants and bulk moduli.

Compared with PBE, PBEsol restores the second-order gradient expansion for exchange in high-density regions and adjusts the exchange-correlation enhancement factors to better describe densely packed electron systems such as metals and ionic solids. This results in improved predictions for crystalline properties, at the cost of some accuracy for molecular systems.

Empirical tests show that PBEsol yields lattice constants and surface energies that are generally closer to experimental values for a wide range of solids. It is commonly used for structural optimization, band-structure calculations, and bulk property predictions in solid-state physics and materials science. However, like other GGA functionals, it is not designed to capture dispersion interactions without additional corrections, and its performance for molecules or weakly bound systems is typically less favorable than that of PBE or hybrid functionals.

Since its introduction in 2008, PBEsol has been implemented in many density functional theory codes and remains a standard option when accurate lattice constants are required for solids.