Dynamic Structure Factor and Dielectric Function of Valence Electrons in Lithium Hydride: An Inelastic X‐Ray Scattering Study at Finite Momentum Transfer

Abstract

The effects of electron–hole interaction in the dynamic structure factor Sfalse(q,ωfalse) and the complex dielectric function ϵfalse(q,ωfalse) of valence electrons in lithium hydride at finite momentum transfer q are investigated by means of inelastic X‐ray scattering (IXS) spectroscopy and ab initio theoretical methods. Calculations of Sfalse(q,ωfalse) and ϵfalse(q,ωfalse) are conducted within time‐dependent density functional theory (TDDFT) in adiabatic local density approximation (ALDA) and many‐body perturbation theory (MBPT) based on the Bethe–Salpeter equation (BSE). The findings reveal that for low q an explicit treatment of electron–hole interactions using BSE formalism slightly modifies the low‐energy structures in Sfalse(q,ωfalse) in comparison with ALDA results but affects strongly the macroscopic dielectric functions. A very good agreement between the experimental and theoretical Sfalse(q,ωfalse) and ϵfalse(q,ωfalse) in all the range of investigated q values is achieved for calculations based on BSE after taking into account the full excitonic Hamiltonian. The results demonstrate the potential of approximations based on the BSE to accurately describe the valence excitation spectra, including the near‐onset region, and the dielectric response in insulating systems, where excitonic effects are relevant.

Electronic excitation spectra of cerium oxides: from ab initio dielectric response functions to Monte Carlo charge transport simulations

“…where ρ is the DFT ground state density. This approach is supported by previous works on inelastic X-ray scattering (IXS) for finite momentum transfer calculations where the ALDA kernel showed a good agreement with the experimental findings due to correct inclusion of short range terms [57][58][59][60] .…”

Energy Deposition around Swift Carbon-Ion Tracks in Liquid Water

“…Even though the Random Phase Approximation (RPA) ( ) provides a reasonable estimation of the macroscopic dielectric matrix, ALDA calculations have shown a general improvement in the agreement with the Inelastic X-Ray Scattering (IXS) experimental results, not only in finite-systems but also in crystalline systems [ 71 , 72 , 73 , 74 , 75 ]. This good TD-LDA (TD-DFT with ALDA kernel) behaviour in describing the IXS is commonly due to the less prominence of excitonic effects in the ELF in contrast to the absorption spectra (the ALDA and APBE omit the ultra-nonlocal term fundamental to represent them in the macroscopic limit, see Ref.…”

Electronic excitation spectra of cerium oxides: from ab initio dielectric response functions to Monte Carlo electron transport simulations

“…This approach is supported by previous studies on inelastic X-ray scattering (IXS) for finite momentum transfer calculations where the ALDA kernel showed good agreement with the experimental findings due to correct inclusion of short range terms. [59][60][61][62] For periodic crystals one can exploit the translational symmetry, and the microscopic dielectric function can be conveniently written in reciprocal space, i.e. e G,G 0 (q, W) = e(q + G, q + G 0 , W), where G and G 0 are the reciprocal lattice vectors, and q is the transferred momentum vector in the first Brillouin zone (1BZ).…”