Theoretical Momentum Distributions in Nb₃O₃

Abstract

The theoretical momentum density distributions (MDD) in NbO measured by Compton profile experiments and positron annihilation techniques are calculated by the APW method. The difference between Compton profile and the positron annihilation profile comes from the trapping of positrons at vacancies. The trapping effect makes the positron annihilation profiles broader a little. In order to express the ground state of a positron in NbO by the APW method, 33 augmented plane waves with at least three angular momentum quantum number terms (l=0, 2 and 4) are found to be necessary. Both the Compton profiles and positron annihilation profiles show anisotropies, but those structures are different from each other. It is shown that the anisotropies are due to the fully occupied bands as well as to the topology of the Fermi surfaces. But folded MDD’s to the first Brillouin zone show the characteristic structures of the Fermi surfaces very well.