非化学计量层状二硼化物M $_{1-x}$ B $_2$（M = Mg，Al，Zr，Nb）的第一性原理原子模型
Atomic models of non-stoichiometric layered diborides M$_{1-x}$B$_2$ (M = Mg, Al, Zr and Nb) from first principles
摘要：
现在假设非化学计量金属二硼化物M $_{1-x}$ B $_2$的两种原子模型：（i）存在阳离子空位和（ii）存在位于阳离子空位位点的“超化学计量”硼。我们用广义梯度近似（GGA）的VASP-PAW方法对交换关联势进行了第一性原理总能量计算，揭示了M $_{1-x}$ B $_2$可能的稳定原子构型随M阳离子类型的变化趋势（M = Mg、Al、Zr或Nb）和缺陷的类型（金属空位与由单原子形式的“超化学计量”硼占据的金属空位，二聚体B $_2$或三聚体B $_3$）。此外，我们已经估计了这些非化学计量状态的稳定性（以镁-硼系统为例）取决于可能的合成路线，即通过固态反应方法，以及固体硼和Mg蒸气之间的反应;以及这些试剂之间的气相。结果表明，B $_2$和B $_3$等非化学计量态在金属位上可以稳定存在，而空位被单个硼原子占据是最不利的.
英文摘要：
Two atomic models of non-stoichiometric metal diborides M$_{1-x}$B$_2$ are now assumed: (i) the presence of cation vacancies and (ii) the presence of 'super-stoichiometric' boron which is placed in cation vacancy site. We have performed first principle total energy calculations using the VASP-PAW method with the generalized gradient approximation (GGA) for the exchange-correlation potential in a perspective to reveal the trends of M$_{1-x}$B$_2$ possible stable atomic configurations depending on the type of M cations (M = Mg, Al, Zr or Nb) and the type of the defects (metal vacancies versus metal vacancies occupied by 'super-stoichiometric' boron in forms of single atoms, dimers B$_2$ or trimers B$_3$). Besides we have estimated the stability of these non-stoichiometric states (on the example of magnesium-boron system) as depending on the possible synthetic routes, namely via solid state reaction method, as well as in reactions between solid boron and Mg vapor; and between these reagents in gaseous phase. We demonstrate that the non-stoichiometric states such as B$_2$ and B$_3$ placed in metal sites may be stabilized, while the occupation of vacancy sites by single boron atoms is the most unfavorable.
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