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Comment on ``Restoring the Density-Gradient Expansion for Exchange in Solids and Surfaces''

Summary: Comment on ``Restoring the Density-Gradient
Expansion for Exchange in Solids and Surfaces''
A recent Letter by Perdew et al. [1] presents a new
functional, PBEsol, intended for solid state and surface
systems. It is based on a gradient expansion of the ex-
change energy and a final fit of the exchange-correlation
(xc) energy to that of surface jellium. The former compo-
nent ``restoring the gradient expansion'' is analyzed exten-
sively and put forward as an explanation for the excellent
results, while the latter, which is a major component of the
AM05 [2,3] density functional, receives little attention. A
brief comparison between AM05 and PBEsol is given in
the supplementary material. The focus is on partial differ-
ences, e.g., how the AM05 exchange functional is far from
reproducing the behavior of the gradient expansion, and
not on the integrated behavior of these two functionals. If
results for AM05 and PBEsol were decidedly different, the
indirect comparison would support the importance of an
exchange functional with the features suggested by Perdew
et al. However, the most striking conclusion from a direct


Source: Armiento, Rickard - Department of Physics, Royal Institute of Technology (KTH)
Burke, Kieron - Department of Chemistry, University of California, Irvine


Collections: Chemistry; Materials Science; Physics