Experimental Determination of the Form and Structure Factor of Molten Lithium

Abstract

The aim of the present paper is to state differences in the spatial distribution of valency electrons for free metal atoms and for molten metals. The element lithium was chosen since both its inner and outer electrons play an important role, so that when a precise X-ray and a precise neutron-diffraction experiment have been carried out a difference, if it exists at all. should be recognizable. The correction of the X-ray data for inelastic, i.e. Compton scattering was done on the basis of an inelastic measurement performed on a spectrometer equipped with a position sensitive detector. The structure factors S (q) calculated from the X-ray and neutron diffraction data show very good coincidence within the whole q-range. Slight deviations for 0 ≦ q ≦ 1.7 Å-1 are discussed but yield no hint at all on electron correlations independent of the nuclei.

Ab initiosimulations of the dynamic ion structure factor of warm dense lithium

“…In particular, the q(k) from the DFT-MD simulations is lower than calculations in Debye-Hückel theory and shows antiscreening for k = (2.5 − 5) Å −1 , as already found in other works [29,38,67]. The result of q(k) in [27] is consistent with Debye-Hückel using Z f = 1.35.…”

“…1, we compare our simulation results at 600 K (∼0.05 eV) with available data from neutron and x-ray scattering experiments [38] performed at T = 595 K and a mass density of 0.495 g/cm 3 which represents an ion number density of n = 0.043 Å −3 . The melting point is at 453 K. Our simulation results agree very well with the experimental data of Olbrich et al [38] for all k values and with an analytical model of Chihara [39]. Furthermore, in the long-wavelength limit, S ii (k → 0) can be calculated via the isothermal compressibility κ T by…”

“…Therefore, we report only quantities averaged over the possible wave vectors with the same magnitude. Static structure factor Sii(k) for liquid lithium at T = 0.495 g/cm 3 from scattering experiments of Olbrich et al [38] at T = 595 K (blue diamond), from an analytical model of Chihara [39] (violet line), and from DFT-MD simulations at T = 600 K (orange line). In the inset, the long-wavelength limit is shown via the isothermal compressibility as determined from separate DFT-MD simulations for T = 600 K (orange circle) and experimental values [38] (blue triangle).…”

Probing ion-ion and electron-ion correlations in liquid metals within the quantum hypernetted chain approximation

“…Measuring these differences will be extremely challenging, since they require two completely different scattering techniques, which implies subtracting two different sets of systematic corrections. In particular, the removal of incoherent scattering effects from the total scattering remains under discussion 35,34,36 . We note that a series of experiments measuring the differences between X-ray and neutron-scattering determinations of S II (k) have been reported for Li 35 , Na, Mg, Al, Zn, Ga, Sn, Te, Tl, Pb, and Bi 37 .…”

The Ion-Electron Correlation Function in Liquid Metals

“…Then the neutron structure factor, SN(Q) which is a measure of the correlations between nuclei in liquid metals, is determined as follows: (2) Similar discussion is applicable to X-ray diffraction by valence electrons and ions. When we use the Ashcroft-Langreth form(13) of the partial structure factors between particles as ions and electrons, Sii(Q), See(Q) and Sie(Q), where i=ion and e=electron, the coherent Xray scattering intensity, IcohX(Q), is written as follows: (3) where fi(Q) is the form factor of an ion and that of a valence electron is considered to be unity, because each valence electron is sufficiently a point charge as an good approximation(1). The physical meaning of the first term in the square bracket of eq.…”