Condensed Matter

Members: Alex Quandt, Daniel Joubert, Izak Snyman, Robert Warmbier,

Density Functional Theory (DFT) is a general approach to the ab initio description of quantum many-particle systems, in which the original many-body problem is rigorously recast in the form of an auxiliary single-particle problem. 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 applies in particular to the ground state energy, which allows to represent the effects of the particle-particle interaction in an indirect form via a density-dependent single-particle potential. In addition to the Hartree (direct) contribution this potential contains an exchange-correlation (xc) component, which is obtained from the so-called xc-energy 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 and time-dependent systems, utilizing the four current and the time-dependent 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. The main areas for applications of DFT are condensed matter and cluster physics as well as quantum chemistry.

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