中文摘要：

采用基于密度泛函理论的Dmol4.1程序包，通过计算替换Mg、形成Mg空位、体系移走H原子所需能量及电子结构的改变，对金属氟化物改善MgH2体系解氢性能的机制进行探讨。结果发现：形成Mg空位所需能量明显高于Fe、Ti、Zr、V、Ni、Nb、Cr、Cu替代Mg所需能量，与形成Mg空位相比，低温下替代Mg更利于MgH2体系解氢；NiF2、NbF5、ZrF4作为催化剂利于MgH2体系解氢，理论计算的强弱顺序与实验结果一致；NiF2、NbF5、ZrF4金属氟化物改善MgH2体系解氢性能主要在于NiF2中的Ni、NbH中的Nb、ZrH2中的Zr分别替代MgH2中的Mg，加速了化学反应：NiF2＋3MgH2=MgF2＋Mg2NiH4、2NbF5＋5MgH2=5MgF2＋2NbH＋4H2、ZrF4＋2MgH2=2MgF2＋ZrH2向右进行，使结构稳定的MgH2发生转变生成了Mg2NiH4、NbH和ZrH2等氢化物。电子态密度的进一步分析结果发现：Ni、Nb、Zr替代MgH2体系中的Mg，使超胞中心原子与其周围第1、2近邻H原子组成的八面体区域，成键的总电子数在费米能级以下按Ni、Ti、Zr的替代顺序增多，表明对应MgH2体系的结构稳定性按Ni、Ti、Zr的替代顺序增强，而解氢按Ni、Ti、Zr的替代顺序在下降，较好解释了NiF2、NbF5、ZrF4利于MgH2体系解氢，理论计算的强弱顺序与实验结果的一致性

英文摘要：

Abstract：The dehydrogenating properties of MgH2 systems were improved by the addition of metal fluorides as the catalyst; the energy of substitution for the Mg atom, the Mg vacancy formation energy, the energy to remove H atoms and electronic structure change of MgH2 systems were calculated by Dmol4.1 program based on the density functional theory. The mechanism of improvement of dehydrogenating properties of MgH2 systems by the addition of metal fluorides was discussed. The results show that the Mg vacancy formation energy is significantly higher than that of Fe, Ti, Zr, V, Ni, Nb, Cr or Cu substitution, which means that the substitution of these elements at the Mg site is more favorable for dehydrogenation of MgH2 system than the Mg vacancy formation at lower temperatures. NiF2, NbF5 and ZrF4 all benefit for the dehydrogenation of MgH2 systems, and the calculation results of improvement of the dehydrogenating properties of MgH2 systems are in agreement with experimental results. The Ni, Nb and Zr atoms replace a Mg atom of MgH2 systems respectively, the corresponding reactions of NiF2＋3MgH2=MgF2＋Mg2NiH4, 2NbF5＋5MgH2=5MgF2＋2NbH＋4H2 and ZrF4＋2MgH2=2MgF2＋ZrH2 are accelerated; therefore, MgH2 with the higher stability can be changed into the other hydrides, such as Mg2NiH4, NbH and ZrH2. Compared with the density of states （DOS） of MgH2 systems, it is found that when the Ni, Nb or Zr atom replaces Mg atom, the valence electron numbers below Fermi level in octahedral areas made of the supercell center atom and its first-nearest, second-nearest H atom increased in the order of Ni, Ti, Zr, meaning the corresponding structural stability are increased while the dehydrogenating properties are reduced, both of which are in the order of Ni, Ti and Zr. A good agreement between the calculation results of the improvement of the dehydrogenating properties of MgH2 systems by NiF2, NbF5 and ZrF4 as the catalyst and experimental results can also be well explained