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The structural, electronic and elastic properties of LaNi 5− x Fe x (x = 0.25, 0.5, 0.75, 1, 1.25) have been investigated employing the density functional theory with the generalized gradient approximation (GGA). The optimized results indicate that Fe prefers to substitute Ni atom in the 3 g site, and Fe replaces 2c site of Ni atom up to x = 1.25. The radius of 6 m interstitial site gradually increases as x goes from 0 to 1.25 due to volume expansion, which is one of the reasons for the increase of hydrogen storage. Combined with elastic constants and elastic modulus, the anti-pulverization ability of the La–Ni–Fe system enhances, and LaNi 4.25 Fe 0.75 has the best anti-pulverization capability among six crystal structures. According to the density of states, the new peak appears at near −5 eV which is dominated by Fe-3d States. Based on the analysis of charge distributions and charge density differences, the sequence of interaction between atoms is Ni 2 c -Fe 3 g > Ni 2 c -Ni 3 g > Ni 3 g -Ni 3 g > Ni 3 g -Fe 3 g > La–Ni 2 c > La–Fe 2 c , while that of the interactions with H atom is as follows: Fe > Ni 3 g > Ni 2 c > La. The electron hybridization of H and La, Ni, Fe atoms form covalent bonds through electron transfer. To study the interaction between Ni, Fe and H atoms, the electronic densities on (0002) plane for LaNi 4.25 Fe 0.75 are plotted in Figure (a). It is obvious that the charge of H atoms overlaps well with that of iron and nickel atoms, and the corresponding electron density between H atom and Ni, Fe atoms is 0.0864, 0.0868 e/bohr3, respectively. It indicates that the chemical bond between H atom and Fe atom is the strongest, which is still shown that La-Ni-Fe system has the good hydrogen fixation capacity.To analyze the electron transfer behavior and bonding features between atoms, the (0002) plane of charge density difference contour is drawn in Figure (b). It is obvious that hydrogen gains electrons while other atoms lose electrons. Generally, the covalent bonds between H and Fe, Ni are formed. Image 1 • Fe prefers to substitute Ni atom in the 3g site, and Fe is replacing 2c site of Ni atom up to x=1.25. • The radius of 6m interstitial site increases gradually as x goes from 0 to 1.25. • The sequence of interaction between atoms is Ni 2c -Fe 3g > Ni 2c -Ni 3g > Ni 3g -Ni 3g > Ni 3g -Fe 3g > La-Ni 2c > La-Fe 2c , and the order of the interactions with H atom is as follows: Fe > Ni 3g > Ni 2c > La. • The elastic constants for LaNi 5-x Fe x (x=0.25, 0.5, 0.75, 1, 1.25) have been successfully obtained. • LaNi 4.25 Fe 0.75 has the best anti-pulverization characteristics among all structures. [ABSTRACT FROM AUTHOR]

The structure, equation of state, mechanical and vibrational properties of single crystals of ices II, VIII, XI and ice in a previously predicted phase bct-4 are studied within the Hartree-Fock method using the density functional theory (B3LYP hybrid functional) with localized Gaussian atomic orbitals as implemented in the "CRYSTAL14" software package. Calculated lattice parameters, elastic moduli of single crystals, and mechanical parameters of polycrystalline samples are shown to meet the criteria of mechanical stability. Parameters of the Vinet equation of state are obtained. Energy band widths and Mulliken atomic charges are determined using obtained energy and spatial distribution of electrons. The frequencies of long-wave vibrations are calculated and vibrational spectra are constructed. [ABSTRACT FROM AUTHOR]