AB-INITIO HARTREE-FOCK STUDY OF LITHIUM AND SODIUM SULFIDES - ELECTRONIC AND SCATTERING PROPERTIES

The electronic structure of lithium sulfide and sodium sulfide in the solid state is established at the Hartree-Fock level, as implemented in the CRYSTAL program. Two all-electron basis sets are adopted for each compound. Mulliken analysis, band structure, density of states and electron charge density are studied: these exhibit the highly ionic character of both compounds; this seems rather surprising because of the weak electronegativity and large polarizability of the sulfur. Form factors of the sulfur are deduced from the structure factors and analysed in order to show the deformations of this anion in the crystal environment. Finally, electron momentum density and Compton profiles confirm the almost fully ionic character of the compounds and prove the quality of the calculated wavefunctions.