Ab initio PP–TT phase diagram of NaBH4

We have studied structural stability of cubic (Fm3̄m) and tetragonal (P4̄21c) phases of NaBH4 in the PP–TT plane. Electronic density of states and dielectric constants (ϵ∞)(ϵ∞), and phonon dispersion curves are also obtained. Well known disordering of [BH4]− tetrahedra in the cubic phase is approximated by 2:2 ordering along [110]. The resulting transition temperature (Tc) at 0 is 133 K, which is similar to the experimental value (Tc=190K). The PP–TT phase diagram is compared with the recently reported experiment for low pressure range, where our result agrees with the experiment qualitatively.