DENSITY-FUNCTIONS AND DENSITY FUNCTIONALS

This paper is concerned with the electron density and other 'property densities' and, through the use of concrete examples, touches upon som e of the fundamental aspects of density functional theory (DFT) that a re seldom considered. In particular, this paper considers what density functions are needed in discussing observable electronic properties a nd what is their role in DFT. The implications of the Pauli Principle and the constraints imposed by the requirement of N-representability a re considered in some detail.