Density Functional Theory
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Characteristic density gradient for Silicon (dia)

Density Functional Theory (DFT) is a general approach to the ab
initio description of quantum manyparticle systems, in which
the original manybody problem is rigorously recast in the form of
an auxiliary singleparticle problem (for an overview see [1]).
For the most simple case of (nondegenerate) stationary problems,
DFT is based on the fact that any ground state observable is uniquely
determined by the corresponding ground state density n, i.e.
can be understood as a functional of n.
This statement in particular applies to the ground state energy,
which allows a representation of the particleparticle interaction
effects in an indirect form via a densitydependent singleparticle
potential.
In addition to the Hartree (direct) contribution, this potential
contains an exchangecorrelation (xc) component, which is obtained
from the socalled xcenergy functional.
The exact density functional representation of this crucial quantity
of DFT is not known, the derivation of suitable approximations being
the major task in DFT.
Extensions of this scheme to relativistic [2] and timedependent [3]
systems, utilizing the four current and the timedependent density as
basic variables, are also available.
Furthermore, a DFT approach to quantum hadrodynamics (as a model
for the relativistic description of nuclei) has been developed [4].
The main areas for applications of DFT are condensed matter and
cluster physics as well as quantum chemistry.
Our research focuses on the development of more accurate density
functional methods and a deeper understanding of the foundations
of relativistic DFT.
Applications to critical classes of systems (like vanderWaals
bond molecules or Mott insulators) serve as a test of new functionals.
In addition, density functional methods are used to study the
structure and dynamics of molecules, clusters and solids.

E. Engel and R. M. Dreizler,
Density Functional Theory: An Advanced Course,
(Springer, Berlin, 2011);

E. Engel,
in: Relativistic Electronic Structure Theory,
Part 1. Fundamentals,
edited by P. Schwerdtfeger
(Elsevier, Amsterdam, 2002), p.524624.

E. K. U. Gross, J. F. Dobson, and M. Petersilka,
Top. Curr. Chem. 181, 81 (1996).

C. Speicher, R. M. Dreizler, and E. Engel,
Ann. Phys. (N.Y.) 213, 312 (1992).
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Last revision: Nov 15, 2009
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