Coherent Atomic Scattering Factors for the Lithium Hydride Crystal Field

Abstract

This paper describes an effort made to evaluate the coherent atomic scattering factors for the lithium and hydride ions as they exist in the LiH crystal field. The two electron wave functions chosen to describe these ions are each in turn optimized in the field of positive and negative point charges arranged as the corresponding ions are arranged in the crystal. Using the orbital exponents obtained from the minimization process, atomic scattering factor calculations are made in the usual way. The factors for ${\mathrm{Li}}^{+}$ are unchanged. Interesting effects are noted for the ${\mathrm{H}}^{\ensuremath{-}}$ scattering factors.The energy of the ions in the field of point charges is related to the crystal cohesive energy. Specifically, neglecting the zero-point energy correction, the calculated open configuration results were -236.3 and -227.4 kcal/mole when compared with computed and experimentally determined free ${\mathrm{H}}^{\ensuremath{-}}$ reference energies, respectively. The experimental cohesive energy is -218.5 kcal/mole.Finally, it was noted that the ${\mathrm{H}}^{\ensuremath{-}}$ ion contracts in the crystal field. A possible explanation for this effect is given.