Density functional theory via density matrices

After a short survey of currently available routes for constructing an idempotent firstorder density matrix as a function(al) of its diagonal element, the electron density p ( r ); recent progress will be surveyed with specific reference to the exchange potential in (a) the Be atom and (b) in the jellium and Bardeen models of a metal surface. In both examples the off‐diagonal density matrix is expressed in terms of its diagonal density only. Finally, a brief discussion will be given of the way the exact exchange‐correlation potential can be written in terms of higher‐order density matrices, the idempotency condition on the first‐order density matrix γ now being replaced by the inequality γ 2 < γ. © 1995 John Wiley & Sons, Inc.