Lithium, compressibility crystal structure

It is possible to make an approximate quantum-mechanical calculation of the forces operating between ions in a crystal and to predict values for the equilibrium interionic distance, the crystal energy, the compressibility, and other properties of the crystal. This calculation has been made in a straightforward manner for lithium hydride (Li+H-, with the sodium chloride structure) hy Hylleraas, with results in good agreement with experiment.10 A thorough theoretical treatment of... 

This very high compressibility is to be expected from the structure of the crystal which, as seen above, is molecular rather than ionic and moreover contains large open spaces between the atoms. The refractive indices at 17° C. are 1-733 for sodium light and 1-748 for lithium light.2 Klocke observed 3 that for yellow light the sublimed crystals exhibit double refraction, but this could not be confirmed by Brauns.4... 

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