Interplay between inelastic X‐ray scattering and ab initio density‐response calculations: Insight into the electronic correlations in aluminum

Inelastic X‐ray scattering (IXS) measurements on Al have been analyzed in conjunction with ab initio , time‐dependent density functional theory (TDDFT) calculations of the electron–hole excitation spectrum. The dynamical structure factor evaluated with use of the many‐body kernel f xc obtained within the adiabatic extension of the local‐density approximation (ALDA) is shown to be in good agreement with the IXS energy‐loss data for energies up to about 20 eV, for momentum transfers up to twice the Fermi wave vector. For larger energy transfers the complex, frequency‐dependent f xc obtained by Devreese and collaborators via dynamical‐exchange decoupling techniques is shown to lead to a description of the IXS data comparable with that of the ALDA. For low energies the ALDA works better, a conclusion with a simple physical interpretation. The analysis of the relative merits of the models for the many‐body interactions is made using IXS cross sections that were obtained in absolute units; to this end, a procedure was introduced which is applicable for arbitrary materials, not just for sp ‐bonded Al.