Studies on the electronic structures of LaNi 5 and LaNi 5H 0.2 by means of the DV-Xα method

Abstract

Electronic structures of hydrogen absorbing metal, LaNi 5 and LaNi 5H 0.2 were studied by means of the DV-Xα method. In the method, the matrix elements of Hamiltonian and overlap integrals in the secular equation are evaluated by the weight sums of integrand values at the discrete sampling points, instead of conventional integration procedure. Because of the number of the sampling point affected the electronic structure such as the bond order between the atoms and the ionicities of atoms in LaNi 5, the appropriate sample point number was examined, and it was found that 800 sample points were sufficient to evaluate the bond order and the ionicity. The cluster size of LaNi 5 also affected the electronic structure, so the suitable cluster size was determined by expanding gradually the cluster size, and the cluster (G) was appropriate to evaluate the electronic structure. The electronic structure of the low hydrogenated cluster (G–H), LaNi 5H 0.2, was also studied, and the electronic structure was compared with that of the cluster (G). The bond orders of La–La, La–Ni(1), La–Ni(2) and La–Ni(3) were similar for both the clusters. The heats of formations of the hydrides of Ni and La are −8.8 kJ/mol H 2 and −208 kJ/mol H 2, respectively, and La has larger affinity with H than Ni in these binary system. However, the H atom interacted more strongly with Ni atoms than La atoms in the cluster (G–H).