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Subsystem functionals in density-functional theory: Investigating the exchange energy per particle R. Armiento*
 

Summary: Subsystem functionals in density-functional theory: Investigating the exchange energy per particle
R. Armiento*
Department of Physics, Royal Institute of Technology, Stockholm Center for Physics, Astronomy and Biotechnology,
SE-106 91 Stockholm, Sweden
A. E. Mattsson
Surface and Interface Sciences Department MS 1415, Sandia National Laboratories, Albuquerque, New Mexico 87185-1415
Received 7 June 2002; published 31 October 2002
A viable way of extending the successful use of density-functional theory into studies of even more complex
systems than are addressed today has been suggested by Kohn and Mattsson W. Kohn and A. E. Mattsson,
Phys. Rev. Lett. 81, 3487 1998 ; A. E. Mattsson and W. Kohn, J. Chem. Phys. 115, 3441 2001 , and is
further developed in this work. The scheme consists of dividing a system into subsystems and applying
different approximations for the unknown but general exchange-correlation energy functional to the different
subsystems. We discuss a basic requirement on approximative functionals used in this scheme; they must all
adhere to a single explicit choice of the exchange-correlation energy per particle. From a numerical study of a
model system with a cosine effective potential, the Mathieu gas, and one of its limiting cases, the harmonic
oscillator model, we show that the conventional definition of the exchange energy per particle cannot be
described by an analytical series expansion in the limit of slowly varying densities. This indicates that the
conventional definition is not suitable in the context of subsystem functionals. We suggest alternative defini-
tions and approaches to subsystem functionals for slowly varying densities and discuss the implications of our
findings on the future of functional development.

  

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

 

Collections: Materials Science; Physics