  The energy landscape of Mg(BH4)2 under pressure is explored by ab initio
evolutionary calculations. Two new tetragonal structures, with space groups P-4
and I41/acd are predicted to be lower in enthalpy, by 15.4 kJ/mol and 21.2
kJ/mol, respectively, than the earlier proposed P42nm phase. We have simulated
X-ray diffraction (XRD) spectra, lattice dynamics, and equations of state (EOS)
of these phases. The density, volume contraction, bulk modulus, and the
simulated XRD patterns of I41/acd and P-4 structures are in excellent agreement
with the experimental results.
