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Phys. Rev. A 76, 040501(R) (2007) [4 pages]

Exchange and correlation in open systems of fluctuating electron number

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John P. Perdew1, Adrienn Ruzsinszky1, Gábor I. Csonka2, Oleg A. Vydrov3, Gustavo E. Scuseria3, Viktor N. Staroverov4, and Jianmin Tao5
1Department of Physics, Tulane University, New Orleans, Louisiana 70118, USA
2Department of Chemistry, Budapest University of Technology and Economics, H-1521 Budapest, Hungary
3Department of Chemistry, Rice University, Houston, Texas 77005, USA
4Department of Chemistry, University of Western Ontario, London, Ontario, Canada N6A 5B7
5Department of Physics, University of Missouri-Columbia, Columbia, Missouri 65211, USA

Received 8 January 2007; published 10 October 2007

While the exact total energy of a separated open system varies linearly as a function of average electron number between adjacent integers, the energy predicted by semilocal density-functional approximations is concave up and the exact-exchange-only or Hartree-Fock energy is concave down. As a result, semilocal density functionals fail for separated open systems of fluctuating electron number, as in stretched molecular ions A2+ and in solid transition-metal oxides. We develop an exact-exchange theory and an exchange-hole sum rule that explain these failures and we propose a way to correct them via a local hybrid functional.

© 2007 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevA.76.040501
DOI:
10.1103/PhysRevA.76.040501
PACS:
31.15.Ew, 71.15.Mb, 71.45.Gm
 
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