Approximate kinetic energy functionals for atoms in extended systems

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Abstract
The applicability of approximate kinetic energy functionals of the electron density n(r) for use in problems involving atoms added to extended host systems is investigated. As well as reexamining the von Weizsacker gradient expansion correction to the Thomas-Fermi kinetic energy, a new gradient correction is proposed which is based on electron gas results and utilises the dominant wave-vector suggested by Langreth and Mehl (1983). These approximate kinetic energy functions are first tested in fully variational calculations on free atoms (Z=1 to 50) with results for ground state energies, (r2) and n(0) compared with corresponding Hartree-Fock values. The models are then used to calculate the embedding energies Delta E of atoms in jellium at density n and the resulting energy curves Delta E(n) for H through Si, Cl and Ar are compared with the curves from corresponding Kohn-Sham-type calculations. Energy curves predicted by these models for Ni, Zr and Pd are also presented. A principal conclusion of this work is that although the gradient corrections do not appear to form universal kinetic energy functionals, models of this type contain features which should prove useful for the study of atoms in inhomogeneous host systems.

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