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How to Tell an Atom From an Electron Gas: A Semi-Local Index of Density Inhomogeneity
 

Summary: How to Tell an Atom From an Electron Gas: A Semi-Local Index of Density
Inhomogeneity
John P. Perdew and Jianmin Tao
Department of Physics and Quantum Theory Group,
Tulane University, New Orleans, Louisiana 70118, USA
Rickard Armiento
Department of Physics, Royal Institute of Technology,
AlbaNova University Center, SE-106 91 Stockholm, Sweden
(Dated: July 8, 2003)
From a global perspective, the density of an atom is strongly inhomogeneous and not at all like
the density of a uniform or nearly-uniform electron gas. But, from the semi-local or myopic
perspective of standard density functional approximations to the exchange-correlation energy,
it is not so easy to tell an atom from an electron gas. We address the following problem: Given
the ground-state electron density n and orbital kinetic energy density in the neighborhood of
a point r, can we construct an "inhomogeneity index" w(r) which approaches zero for weakly-
inhomogeneous densities and unity for strongly-inhomogeneous ones? The solution requires not
only the usual local ingredients of a meta-generalized gradient approximation (n, n, 2
n,),
but also and 2
. The inhomogeneity index is displayed for atoms, and for model densities

  

Source: Armiento, Rickard - Department of Physics, Royal Institute of Technology (KTH)

 

Collections: Materials Science; Physics