Fan Changzeng, Jin Ye, Li Jian, Dong Xu
State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China.
Sci Rep. 2014 Nov 11;4:6993. doi: 10.1038/srep06993.
Potential crystal structures of BeB2 were explored using ab initio evolutionary simulations. A new phase with a Cmcm space group was uncovered. It was determined that the Cmcm phase is mechanically and dynamically stable and has a lower enthalpy, from ambient pressure up to 13 GPa, than any previously proposed phases, as measured using first-principles calculations. The crystal structure, phonon dispersion, phase transitions, and mechanical and electronic properties of this phase were investigated. It was determined that the Cmcm phase may transform into the phase at pressures higher than 13 GPa. The band structures and density of states reveal that the Cmcm phase is metallic. In addition, the Vickers hardness was calculated using three empirical models. To explain the origin of the hardness, charge density difference maps and a Mulliken population analysis were carried out, which demonstrated that there are strong covalent interactions between B atoms. By analyzing the Crystal Orbital Hamilton Population (COHP) diagrams, it was determined that the total interaction of the Be-B bonds is stronger than that of the B-B bonds, indicating a very complex bonding feature in the new phase. It was predicted that the new Cmcm phase is nearly absent of superconductivity.
利用从头算演化模拟探索了BeB₂的潜在晶体结构。发现了一种具有Cmcm空间群的新相。通过第一性原理计算确定，从环境压力到13 GPa，Cmcm相在力学和动力学上是稳定的，并且比任何先前提出的相具有更低的焓。研究了该相的晶体结构、声子色散、相变以及力学和电子性质。确定Cmcm相在高于13 GPa的压力下可能转变为其他相。能带结构和态密度表明Cmcm相是金属性的。此外，使用三种经验模型计算了维氏硬度。为了解释硬度的起源，进行了电荷密度差图和穆利肯布居分析，结果表明B原子之间存在强共价相互作用。通过分析晶体轨道哈密顿布居（COHP）图，确定Be-B键的总相互作用强于B-B键，这表明新相中存在非常复杂的键合特征。预测新的Cmcm相几乎不存在超导性。
