Electronic structure, phase stability, and chemical bonding in Th2Al and Th2AlH4

Article

关键词: GENERALIZED GRADIENT APPROXIMATION;    GROUND-STATE PROPERTIES;    NEUTRON-DIFFRACTION;    CRYSTAL-STRUCTURE;    HYDRIDES;    SYSTEMS;    SOLIDS;    ALLOYS;    NB;    ZR;   

DOI  :  10.1103/PhysRevB.65.075101

来源: SCIE

【 摘 要 】

We present the results of a theoretical investigation on the electronic structure, bonding nature, and ground-state properties of Th2Al and Th2AlH4 using generalized-gradient-corrected first-principles full-potential density-functional calculations. Th2AlH4 has been reported to violate the 2-Angstrom rule for H-H separation in hydrides. From Our total-energy as well as force-minimization calculations, we found a shortest H-H separation of 1.95 Angstrom in accordance with recent high-resolution powder neutron-diffraction experiments. When the Th2Al matrix is hydrogenated, the volume expansion is highly anisotropic, which is quite opposite to other hydrides having the same crystal structure. The bonding nature of these materials is analyzed in terms of density of states, crystal-orbital Hamiltonian population, and valence-charge-density analyses. Our calculation predicts a different nature of the bonding between the H atoms along a and c. The strongest bonding in Th2AlH4 is between Th and H along c which form dumbbell-shaped H-Th-H subunits. Due to this strong covalent interaction there is a very small amount of electrons present between the H atoms along c. This reduces the repulsive interaction between the H atoms along c and explains why Th2AlH4 has a shorter H-H separation than most other metal hydrides. The large difference in the interatomic distances between the interstitial regions where one can accommodate H in the ac and ab planes along with the strong covalent interaction between Th and H are the main reasons for highly anisotropic volume expansion on hydrogenation of Th2Al.

【 授权许可】

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