Structural stability of complex hydrides: LiBH4 revisited.

A systematic approach to study the phase stability of LiBH4 based on ab initio calculations is presented. Three thermodynamically stable phases are identified and a new phase of Cc symmetry is proposed for the first time for a complex hydride. The x-ray diffraction pattern and vibrational spectra of the Cc structure agree well with recently reported experimental data on LiBH4. Calculations of the free energy at finite temperatures suggest that the experimentally proposed P6(3)mc phase is unstable at T>0 K.