A theoretical study of Compton scattering for MgO. I. Momentum density, Compton profiles, and B-functions

Abstract

On the basis of augmented-plane-wave band-structure calculations for the insulating compound MgO the authors have calculated the momentum density. Compton profiles, and B(z) functions. In order to derive physical insight from the results they have put much effort into understanding the momentum density in terms of real-space wavefunctions and nearest-neighbour interactions. To this end they performed a backtransformation of the momentum densities into real space, thus obtaining Wannier-like functions. The Compton profile and the B(z) function along (100) are distinctly different from the ones along the other two main directions, and this is also revealed by the experimental results. However, there is a significant discrepancy between the results and experiment for the B(z) function along (100). A similar discrepancy is also observed by another calculation using a different model. The source of this discrepancy is not understood.

The electronic structure of NaF and CaO studied by Compton scattering

“…1, both with the experimental anisotropy showing the largest deviations at small Pz and also for the largest peak at 1-2 a.u. Similar deviations were found for MgO (Aikala et al, 1982;Podloucky & Redinger, 1984). This is surprising for NaF, because it is supposed to be an almost ideal candidate for an ionic crystal and because in the case of the spherically averaged Compton profiles the agreement between the experiment and LCAO model was good (Paakkari & Halonen, 1978).…”

“…In our previous study on MgO (Aikala, Paakkari & Manninen, 1982;Podloucky & Redinger, 1984) we found a discrepancy between the experimental data and both LCAO and APW theories expressed in terms of the Compton profile and autocorrelation function. Despite the laborious effort, including the use of various kinds of wave functions for the 02-ion, the problem was not solved.…”

“…One should remember, however, that the differences resulting from the use of various 0 2-wave functions are much smaller than the general discrepancy between the LCAO model and experiment in CaO. (Aikala, Paakkari & Manninen, 1982;Podloucky & Redinger, 1984). In view of the Compton-profile differences shown in Figs.…”

Electron charge density and electron momentum distribution in magnesium oxide

“…In a recent paper Podloucky & Redinger (1984) reported electron momentum distribution (EMD) and Compton profile curves for MgO as obtained by an augmented-plane-waves calculation. Unfortunately the data are not tabulated, so that a point-topoint comparison is impossible; nevertheless, the essential features in the three directions are very similar to the present ones: the [111] curve is intermediate between the other two; the peak in the [100] direction is the broadest, and is shifted to higher (Weiss, 1970;Togawa et al, 1971) are quite unreliable because of the fact that with X-rays multiple scattering events are important, and the impulse approximation fails for 1 s electrons, useful information is provided by more recent y-ray measurements (Berggren et al, 1977;Aikala et al, 1982).…”

“…On the other hand, residual experimental errors could be at the origin of the difference; in this respect it must be noticed that at low momenta Aikala's curve is appreciably lower (and nearer to ours) than the lessrecent one (Berggren et al, 1977). A deeper comparison with the experimental data, and with the theoretical results of Podloucky & Redinger (1984), including an analysis of the anisotropy, of the autocorrelation function (Schiilke, 1977;Pattison & Williams, 1976), and of basis-set effects would require much more space and is deferred to another paper.…”