高压下Ca(BH_4)_2晶体结构相变的第一性原理研究

High-pressure phase transitions in Calcuim Borohydride from first-principles calculations

基于密度泛函理论第一性原理的赝势平面波方法,研究了高压下Ca(BH_4)_2的相变行为.研究结果表明,当压强点为3.72GPa时,高压相β-Ca(BH_4)_2的空间群为P4结构,相变时伴随4.4%的体积坍塌.电子态密度分析表明,Ca(BH_4)_2是具有5.0eV带隙的绝缘体.根据电荷转移和密立根布局分析表明,Ca(BH_4)_2在相变时电荷主要由Ca原子向BH_4单元转移,Ca^(2+)与[BH_4]-单元之间存在离子相互作用,单元内部B与H原子间形成共价键.

The phase transformation behavior of Ca（BH4）2 under high pressure is investigated, using the first principle of the plane wave pseudo-potential technology based on the density function theory（DFT）. The results indicates that high-pressure β-Ca（BH4）2 phase become space group P4^- with the volume contraction of 4.4% when pressure-induced structural phase transition happened at 3.72 GPa. The analysis of electronic density of states showed that β-Ca（BH4）2 possess nonmetallic character with finite energy gaps of 5.0 eV. Moreover, according to the analysis of the charge transfer and Mulliken population analysis, electrons are transferred from the calcium atom to the [BH4]- unit when β-Ca（BH4）2 phase transformation takes place. In addition, there exists ionic interaction between Ca2＋ and [BH4]- unit, covalent bond formed between B and H atoms within the unit.