The three-dimensional electron momentum density ρ(p) in Li is reconstructed via a direct Fourier transform method which is free from functional assumptions concerning the shape of ρ(p). For this purpose, 12 high-resolution Compton profiles are measured, and corresponding highly accurate computations carried out within the band theory framework. Extensive comparisons between the ρ(p)’s reconstructed from the theoretical and experimental profiles with each other and with the true (without reconstruction) underlying computed ρ(p) are used to gain insight into the accuracy of our procedures, and to delineate the effects of various parameters (filtering, resolution, eTc.) on the reconstructed ρ(p). The propagation of errors is considered in detail, and a general formula appropriate for the present direct Fourier method is derived. The experimental ρ(p) (in comparison to the theoretical results) shows a substantially more smeared out break at the Fermi momentum pf, and a shift of spectral weight from below to above pf, clearly indicating the importance of electron correlation effects beyond the 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 ρ(p) in the presence of finite resolution is examined at length. The experimental Fermi surface and its asphericity is in good overall accord with theoretical predictions, except that band theory predicts a bulging of the Fermi surface along the [110] direction, which is greater than seen in the measurements; however, our analysis suggests that the set of 12 directions used in the present experiments may not be optimal (in number or orientations) for observing this rather localized Fermi-surface feature.


Originally published in Physical Review B v.63 (2001): 045120. DOI: 10.1103/PhysRevB.63.045120


electron momentum density, Fourier transform method, Compton profiles, Fermi surface

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Lithium, Scattering (Physics), Fourier transformations




American Physical Society

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Copyright 2001 American Physical Society.

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American Physical Society

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