Klaas J. H. Giesbertz, Robert van Leeuwen, Ulf von Barth
We develop a non-local density functional by a direct modeling of the shape of exchange-correlation (xc) hole in inhomogeneous systems. The functional is aimed at giving an accurate xc-energy and an accurate corresponding xc-potential even in difficult near-degeneracy situations such as molecular bond breaking. In particular we demand that: (1) the xc hole properly contains -1 electron, (2) the xc-potential has the asymptotic -1/r behavior outside finite systems and (3) the xc-potential has the correct step structure related to the derivative discontinuities of the xc-energy functional. These demands are achieved by screening the exchange hole in such a way that the pair-correlation function is symmetric and satisfies the sum-rule. These two features immediately imply (1) and (2) while the explicit dependence of the exchange hole on the Kohn--Sham orbitals implies (3). For the dissociating hydrogen molecule, we obtain much improved xc holes and thus also improved binding energies at different interatomic distances, as compared to the local density approximation.
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http://arxiv.org/abs/1210.1800
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