Physics – Chemical Physics
Scientific paper
2012-03-11
Physics
Chemical Physics
Scientific paper
The dimensionless inhomogeneity parameter, $\alpha$, characterizing the extent of orbital overlap, is disentangled for the first time, by the means of separability assumption, from the other dimensionless inhomogeneity parameter, s, the reduced density gradient,in the construction of a meta generalized gradient approximation (MGGA) for the exchange functional. We show that the formation of the intershell region between the outermost core and the valence of an atom within a solid is associated with an increase of $\alpha$ and a decrease of $s$. This observation leads to a simple MGGA exchange functional, which interpolates between the single-orbital regime, where $\alpha=0$, and the slowly varying density regime, where $\alpha \approx 1$, and then extrapolates to $\alpha \to \infty$. The exchange enhancement factor penalizes the formation of the intershell region by increasing monotonically with $s$ and decreasing monotonically with $\alpha$. When combined with a variant of the Perdew-Burke-Erzerhof (PBE) GGA correlation, the resulting MGGA performs equally well for atoms, molecules, surfaces, and solids, and respects a tight Lieb-Oxford bound.
Ruzsinszky Adrienn
Sun Jianwei
Xiao Bing
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