Communication: Effect of the orbital-overlap dependence in the meta generalized gradient approximation

We study for the first time the effect of the dependence of meta generalized gradient approximation (MGGA) for the exchange-correlation energy on its input, the kinetic energy density, through the dimensionless inhomogeneity parameter, a, that characterizes the extent of orbital overlap. This leads to a simple MGGA exchange functional, which interpolates between the single-orbital regime, where alpha = 0, and the slowly varying density regime, where alpha approximate to 1, and then extrapolates to alpha -> infinity. When combined with a variant of the Perdew-Burke-Ernzerhof GGA correlation, the resulting MGGA performs equally well for atoms, molecules, surfaces, and solids. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4742312]