Structure and stability of complex metal hydrides - theoretical approach

摘要

In this paper systematic approach to study the structural stability of the complex hydride, LiBH_4 is presented. The ground state energies of various symmetry structures are determined by means of Density Functional Theory. Simulated annealing method is used to confirm if ground state structures represent real energy minima. The vibrational spectrum and temperature dependence of the free energy of the structures with the lowest energies is determined. Calculated Raman active modes for three symmetries are presented. We show that at high temperatures LiBH_4 possesses monoclinic symmetry and some of the low energy structures are unstable with respect to atomic vibrations. Our studies point to the necessity of calculation of the phonon spectra for complex metal hydrides that contain covalently bounded hydrogen.