掺杂元素对Mg2NiH4稳定性影响的第一性原理研究

本文采用基于密度泛函理论(DFT)的第一原理赝势平面波(PW-PP)方法，计算了低温相Mg2NiH4和(Mg2Ni,X)H4(X=Ag, Al, Ti或Zr)的生成热及电子结构，分析了掺杂元素对Mg2Ni氢化物稳定性的影响. 结果表明，掺杂导致了合金氢化物生成热的绝对值降低，合金氢化物的稳定性下降，且发现掺杂元素电负性越大，氢化物越不稳定. 从电子态密度图和Mulliken布居数分析知道，掺杂后合金氢化物释氢能力增强的主要原因在于Ni-H之间的成键减弱，以及掺杂元素诱导费米能级EF处电子数浓度N(EF)的增加.

First-principles investigations of the influence of alloying elements on the stability of Mg2NiH4

The heat of formation and electronic structures of LT-Mg2NiH4 and (Mg2Ni,X)H4(X=Ag, Al, Ti or Zr) were calculated by plane wave pseudopotential (PW-PP) method which is based on density functional theory, and the influences of alloying elements on the stability of Mg2Ni hydride were investigated. A low absolute value of the negative heat of formation of (Mg2Ni,X)H4(X=Ag, Al, Ti or Zr) compared with that of Mg2NiH4 indicates that the alloying atoms X(X=Ag, Al, Ti or Zr) befit to improve the dehydrogenating properties of Mg2NiH4. An interesting trend is found that, the more electronegative of alloying elements, the more unstability of hydride systems. According to the densities of states and Mulliken population analysis, it was found that the improvement of the dehydrogenating properties of Mg2NiH4 originates from the increasing of the densities of electron numbers N(EF) at Fermi level (EF) and the weaker bonding between Ni and H of (Mg2Ni,X)H4(X=Ag, Al, Ti or Zr) which is caused by the addition of Ag, Al, Ti or Zr atoms. Hence, the dehydrogenating properties of Mg2NiH4 are expected to be improved to a different extent by the addition of alloy elements.