First-principles calculation of the shock-wave equation of state of isotopic lithium hydrides

The equations of state (EOS) of solid LiH in the B1 (NaCl-type) and B2 (CsCl-type) structures have been calculated within the local-density approximation (LDA), using the augmented-plane-wave method with Ceperley-Alder's form for the exchange-correlation energy. Using the EOS obtained by the LDA, the volume dependencies of the Debye temperatures for both phases have been determined. The calculated Debye temperatures in the B1 phase at zero pressure and zero temperature are 1246 K for ⁷LiH and 972 K for ⁷LiD in agreement with the experimental values in the T=0 K limit at normal pressure which are 1190±{}80 K for ⁷LiH and 1030±{}50 K for ⁷LiD, respectively. The calculated lattice constants for isotopic LiH at zero pressure are in agreement with the experimental values at T=83 K by 1.9%. With these results the shock-wave equations of state (the Hugoniot) for both phases have been calculated. The Hugoniots for the B1 phase are in agreement with the experiment by Marsh.