Mg17 Al12、Al2Ca、Al2Nd、Al2Er金属间化合物稳定性与电子结构的第一性原理研究

Study on Structural Stabilities and electronic structure of Mg17Al12、Al2Ca、Al2Nd、Al2Er intermetallic compounds by first principles

摘要:

采用基于密度泛函理论的Castep程序软件包，优化了Mg17Al12、Al2Nd、Al2Er及Al2Ca相晶胞结构，计算了化合物的形成热、结合能和态密度等，分析了化合物结构稳定性与其电子结构的内在联系。结果表明:四种化合物的形成热和结合能均为负值，且化合物的合金化能力和结构稳定性强弱顺序依次为Al2Er、Al2Nd、Al2Ca、Mg17Al12。态密度结果表明: Al2Er和Al2Nd具有较强结构稳定性的主要原因是（1）在费米面低能级区Al(3p)轨道分别与Nd(4f)、(5d)和 Er(4f)、(5d)轨道价电子发生强烈杂化作用；（2）Al2Nd和Al2Er成键电子数较多；（3）这两种化合物的电子参与成键能力较大。电荷密度结果表明：Mg17Al12、Al2Ca、Al2Nd、Al2Er中均存在金属键、离子键、共价键，四种化合物中Al2Er、Al2Nd共价键较强，Al2Ca离子键最强，Mg17Al12中以较强的金属键为主。

Abstract:

The structural stabilities and electronic structures of Mg17Al12, Al2Ca, Al2Nd and Al2Er intermetallic compounds have been investigated by Castep module based on the density functional theory. The heats of formation, cohesive energies and densities of states (DOS) of these compounds are calculated and the crystal structures are optimized. Results show that the heats of formation and cohesive energies are all negative. The Al2Er has the strongest alloying ability and structural stability, then Al2Nd, thirdly Al2Ca and finally Mg17Al12. The calculated DOS of all the compounds in this study shows that Al2Er and Al2Nd exhibit the stronger structural stabilities and the reason can be deduced as follows: (1) The valence electrons between Al (3p) and Er (4f), Al (3p) and Er (5d), Al (3p) and Nd (4f), Al (3p) and Nd (5d) orbits hybrid seriously in the lower energy region below Fermi level. (2) The bonding electron numbers of Al2Nd and Al2Er are more than Al2Ca and Mg17Al12. (3) The bonding abilities of Al2Nd and Al2Er are stronger. Moreover, the calculations of density of charge indicate that all of these compounds contain metallic, ionic and covalent bonds. In these compounds, Al2Er and Al2Nd have the stronger covalent bonds than Al2Ca and Mg17Al12, while the Al2Ca has the strongest ionic bonds and the Mg17Al12 is dominated by the metallic bond.