Charge and momentum density in metals and alloys

Abstract

Following a brief summary of results on the charge density and one-body potential in the light metals Li and Be, the paper is concerned with two specific properties of random alloys, (1) the (integrated local) density of states , the brackets denoting the random configurational average, and (2) the momentum distribution. For the disordered α brasses, the virtual crystal approximation works quite well for some Fermi surface properties, though it appears at first sight to do the configurational averaging in the wrong order. By constructing a periodic potential to yield the generalized partition function of the random alloy (β = 1/kBT), where is the inverse Laplace transform of , some justification is given for the use of such averaging as in the virtual crystal approach. Finally, the momenta of electrons in metallic alloys are studied via two limiting models. First, for cases with charge transfer and localized screening by perturbed “molecular” or Bloch orbitals (e.g., LiMg) Friedel'sThomas Fermi model for concentrated alloys is shown to lead to high-momentum components due to the localized screening charge. Compton scattering ought therefore to give direct information on such screening in an alloy like LiMg. An alternative scheme based on “atoms in crystals” is briefly sketched, and some experimental results on the Compton profile of TiNi alloys are referred to in connection with this latter model.