title: Density functional study of electronic, bonding, and vibrational properties of Ca(NH2BH3)2.
abstract: We present structural, electronic, bonding and vibrational properties of new type hydrogen storage material calcium amidoborane Ca(NH(2)BH(3))(2) by first principles density functional theory using plane wave pseudopotential method. The calculated ground state properties are in good agreement with experiments. The computed Bulk modulus of Ca(NH(2)BH(3))(2) is found to be 28.7 GPa which is slightly higher than that of NH(3)BH(3) indicating that the material is hard over NH(3)BH(3). From the band structure calculations, the compound is found to be a direct band gap insulator with a band gap of 3.27 eV at the Γ point. The calculated band structure shows that the top of the valance band is from the p states of N and the bottom of the conduction band is from d states of Ca. The Mulliken bond populations, Born effective charges and charge density distributions are used to analyze the bonding nature of the compound. It is found that the N-H and B-H bonds are covalent in nature. Further we also compared the phonon density of states and vibrational frequencies of Ca(NH(2)BH(3))(2) with NH(3)BH(3). The study reveals that in both the cases the heavier mass atoms Ca, N, B are involved in the low frequency vibrations whereas the higher frequency vibrations are from H atoms. It is also observed that the vibrational frequencies of B-H bonds are soft in Ca(NH(2)BH(3))(2) when compared to NH(3)BH(3) and thereby concluded that Ca(NH(2)BH(3))(2) is a potential hydrogen storage material for fuel cell applications when compared to NH(3)BH(3).
authors.affiliation: School of Physics, University of Hyderabad, India.
authors.forename: Ch Bheema
authors.initials: ChB
authors.lastname: Lingam
authors.forename: K Ramesh
authors.initials: KR
authors.lastname: Babu
authors.forename: Surya P
authors.initials: SP
authors.lastname: Tewari
authors.forename: G
authors.initials: G
authors.lastname: Vaitheeswaran