Sur l'énergie au zéro absolu de l'hydride et du deutéride du lithium

The zero point energy of the crystals of LiH and LiD is approximated in two different ways. In the first place a formula of London, found by quantisation of the mean free path in condensed systems of rigid spheres, is applied. Adjusting a parameter so as to find the right difference of lattice constants between LiH and LiD yields reasonable values of the zero point energy. In the second place, in a purely theoretical investigation of the lattice vibrations by means of the general theory of Lyddane and Herzfeld for polar crystals of the sodium chloride type, the zero point energies of ( E₀) _LiH = 5,49 kilocalories/mol and ( E₀) _LiD = 4,30 kilocalories/mol are calculated. The origins of these high values and the limitations of the theory are discussed.