Density functional theory in relation to x‐ray and neutron scattering experiments

Abstract

X-ray scattering allows, for example, the ground-state electron density of a crystal, say hexagonal close-packed Be, or a molecular solid, to be extracted. Two routes will be discussed by means of which progress should prove possible on fundamental aspects of density functional theory, given such information on the electron density. In the first of these, the proposal is to extract from X-ray scattering data a function of the density which generalizes the concept of a local density approximation. Specifically, in a closed-shell atom, such as Kr or Xe, the monotonic decay of the electron density from the nucleus is exploited to propose a generalization of local density theories such as Thomas–Fermi, plus Dirac–Slater exchange together with Gell-Mann and Brueckner correlation. In the second route considered, an essentially experimental area termed quantum crystallography is brought into contact with the density matrix approach to density functional theory proposed by Holas and March. Here, though functions of the density are not presently extractable from crystal Bragg reflection data, a method is summarized, due to Holas and this writer, whereby the exchange–correlation potential can be extracted for a given crystal such as Be. This is possible by generalizing the approach of quantum crystallography to include a potential-locality constraint. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 551–557, 1998