Quantum Monte Carlo calculation of Compton profiles of solid lithium

Abstract

Recent high resolution Compton scattering experiments in lithium have shown significant discrepancies with conventional band theoretical results. We present a pseudopotential quantum Monte Carlo study of electron-electron and electron-ion correlation effects on the momentum distribution of lithium. We compute the correlation correction to the valence Compton profiles obtained within Kohn-Sham density functional theory in the local density approximation and determine that electronic correlation does not account for the discrepancy with the experimental results. Our calculations lead do different conclusions than recent GW studies and indicate that other effects (thermal disorder, core-valence separation etc.) must be invoked to explain the discrepancy with experiments.

Reconstructed three-dimensional electron momentum density in lithium: A Compton scattering study

“…[29][30][31][32][33][34] It is difficult to explain such a low value of Z k within the framework of the plasmaron-type physics underlying the conventional picture of the interacting electron gas. [35][36][37][38][39] We note, however, that the analysis of Compton data from a series of LiMg disordered alloys by Stutz et al 11 hinted that the behavior of Li may be idiosyncratic rather than being representative of metals more generally.…”

Calculation of valence electron momentum densities using the projector augmented-wave method

“…In general, however, comparisons have shown that there are systematic anisotropic discrepancies between theory and experiment. As already noted, momentum densities have been calculated using the QMC methods [26,27] and the GW approximation [9,10,25]. However, in the case of Si [26], and Li [27] (QMC) and Li [38,25] (GW ) the correlation correction is not found to differ appreciably from the LP corrected LDA results [31].…”

“…[48] have been calculated with the KKR band structure scheme and the LDA. The momentum density of Li has also been calculated using the LMTO method [17,18], the FLAPW method [9,10,11], the GW approximation [9,10,25], and quantum Monte Carlo methods [27]. Theoretical calculations based on the LDA have failed to describe the momentum density of Li also when the Lam-Platzman correlation correction has been taken into account [48].…”

“…As already noted, momentum densities have been calculated using the QMC methods [26,27] and the GW approximation [9,10,25]. However, in the case of Si [26], and Li [27] (QMC) and Li [38,25] (GW ) the correlation correction is not found to differ appreciably from the LP corrected LDA results [31]. Wakoh et al [39] have shown that the theoretical Compton profiles of Al can be fitted to the experiment using a phenomenological energy-dependent occupation number instead of the LP correction.…”

“…The Hartree-Fock method has also been applied [12,24], and the GW approximation [9,10,25], as well as quantum Monte Carlo (QMC) methods [26,27] which go beyond the DFT and the LDA. The PAW scheme has obvious advantages compared with many of these schemes.…”