Reconstructed three-dimensional electron momentum density in lithium: A Compton scattering study - art. no. 045120

The three-dimensional electron momentum density rho (p) in Li is reconstruc ted via a direct Fourier transform method which is free from functional ass umptions concerning the shape of rho (p). For this purpose, 12 high-resolut ion Compton profiles are measured, and corresponding highly accurate comput ations carried out within the band theory framework. Extensive comparisons between the rho (p)'s reconstructed from the theoretical and experimental p rofiles with each other and with the true (without reconstruction) underlyi ng computed rho (p) are used to gain insight into the accuracy of our proce dures, and to delineate the effects of various parameters (filtering, resol ution, etc.) on the reconstructed rho (p). The propagation of errors is con sidered in detail, and a general formula appropriate for the present direct Fourier method is derived. The experimental rho (p) (in comparison to the theoretical results) shows a substantially more smeared out break at the Fe rmi momentum p(f), and a shift of spectral weight from below to above p(f), clearly indicating the importance of electron correlation effects beyond t he local-density approximation for a proper description of the ground-state momentum density. The question of deducing Fermi-surface radii in terms of the position of the inflection point in the slope of rho (p) in the presen ce of finite resolution is examined at length. The experimental Fermi surfa ce and its asphericity is in good overall accord with theoretical predictio ns, except that band theory predicts a bulging of the Fermi surface along t he [110] direction, which is greater than seen in the measurements; however , our analysis suggests that the set of 12 directions used in the present e xperiments may not be optimal (in number or orientations) for observing thi s rather localized Fermi-surface feature.