The electronic and magnetic structures of $ {rm ScFe_2} $ and of its dihydride $ {rm ScFe_2H_2} $ are self-consistently calculated within the density functional theory (DFT) using the all electron augmented spherical wave (ASW) method with the local
spin density approximation (LSDA) for treating effects of exchange and correlation. The results of the enhancement of the magnetization upon hydrogen insertion are assessed within an analysis of the chemical bonding properties from which we suggest that both hydrogen bond with iron and cell expansion effects play a role in the change of the magnitude of magnetization. In agreement with average experimental findings for both the intermetallic system and its dihydride, the calculated Fermi contact terms $H_{FC}$ of the $^{57}$Fe Mossbauer spectroscopy for hyperfine field, at the two iron sites, exhibit an original inversion for the order of magnitudes upon hydriding.
Investigations within the local spin density functional theory (LSDF) of the intermetallic hydride system $ {rm CeRhSnH_x} $ were carried out for discrete model compositions in the range $ 0.33 leq x_H leq 1.33 $. The aim of this study is to assess t
he change of the cerium valence state in the neighborhood of the experimental hydride composition, $ {rm CeRhSnH_{0.8}} $. In agreement with experiment, the analyses of the electronic and magnetic structures and of the chemical bonding properties point to trivalent cerium for $ 1 leq x_H leq 1.33 $. In contrast, for lower hydrogen amounts the hydride system stays in an intermediate-valent state for cerium, like in $ {rm CeRhSn} $. The influence of the insertion of hydrogen is addressed from both the volume expansion and chemical bonding effects. The latter are found to have the main influence on the change of Ce valence character. Spin polarized calculations point to a finite magnetic moment carried by the Ce $ 4f $ states; its magnitude increases with $ x_H $ in the range $ 1 leq x_H leq 1.33 $.
