Ca(BH_4)_2络合物电子结构及热力学稳定性的第一性原理研究

First-principle studies on electronic structure and thermodynamic stability of Ca(BH_4)_2 complex

利用第一性原理研究了低温及高温相Ca(BH_4)_2络合物的电子结构、晶格振动及其反应焓.计算结果表明:低温及高温相Ca(BH_4)_2中Ca^(+2)与[BH_4]^-以离子键形式相结合,[BH_4]^-离子中B原子和H原子以共价键形式相结合,对该共价键有贡献的主要是B原子的2p轨道电子,H原子的1s轨道电子.Ca(BH_4)_2可能的反应路径为:Ca(BH_4)_2→2CaH_2+CaB_6+10H_2,该反应在300 K下反应焓为43.22 kJ/molH_2.拉伸B—H键所对应的声子频率较高,其值为2360～2500 cm^(-1),这可能是导致B—H键断裂释放氢气需要较高温度的主要原因之一.

The electronic structure, lattice dynamic and reaction enthalpies of low-temperature and high-temperature phases of Ca（BH4）2 complex have been studied using first-principle. The calculation results show that, for both low and high-temperature phases of Ca（BH4）2 complex, the interaction between Ca^＋2 and [BH4]^- anion has an ionic character, and the interaction between B and H is covalent. This covalent bond is dominated by B 2p and H 1s orbitals. The possible dehydrogenation process is 3Ca（BH4）2→2CaH2＋CaB6＋10H2, and the reaction enthalpy is 43.22 kJ/mol H2. The lattice dynamic calculations show that the phonon modes of stretching [BH4]^- anion are in 2360-2500 cm^-1 , these high phonon modes indicate that they need high energies to breakup of B-H bond in [BH4]^- anion.