采用基于密度泛函理论的第一性原理方法,通过计算MgH2两种不同表面((001)和(110))的几何、能态及电子结构,考察其表面稳定性、解氢热力学及其与微观原子及电子结构间的内在关系.结果显示:MgH2(001)和MgH2(110)表面均未发生结构重构现象,两者均为MgH2晶体的稳定解理面,相比而言,MgH2(110)表面具有更高的结构稳定性.平均解氢焓与单H原子解离焓的计算结果表明,MgH2(001)表面具有较佳的解氢热力学.原子及电子结构分析表明,MgH2表面的结构稳定性和解氢热力学与表面H、Mg原子各自的配位数以及体系在费米能级附近的能隙密切相关,即较少的配位数与较窄的能隙对应着表面较低的结构稳定性与较佳的解氢热力学性能.
@@@@Using first-principles method based on the density functional theory, the geometries, energetic and electronic structures of two different MgH2 (001) and (110) surfaces were calculated to investigate the surface stabilities, dehydrogenation thermodynamics and their intrinsic relations with the micro-atomic and micro-electronic structures. The results show that no apparent reconstruction occurs either for MgH2(001) surface or for MgH2(110) counterpart, which suggests that both of them are stable cleavage planes of MgH2 crystal. Comparatively, MgH2(110) surface exhibits a higher structural stability. The calculations of average desorption enthalpy and single H atom dissociation enthalpy show that MgH2(001) surface presents better dehydrogenation thermodynamics. The analysis of atomic and electronic structures implys that the structural stabilities and dehydrogenation thermodynamics of MgH2 surface are closely associated with the respective coordination number of H and Mg atoms located at surface layer as well as the energy gap near Fermi energy level of the system. Namely, the fewer coordination number and the narrower energy gap mean the lower structural stability and the better dehydrogenation thermodynamics of the surface.
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