Investigation of the Adsorption and Diffusion of Hydrogen in Iron Clusters by the Method of Density Functional
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INVESTIGATION OF THE ADSORPTION AND DIFFUSION OF HYDROGEN IN IRON CLUSTERS BY THE METHOD OF DENSITY FUNCTIONAL V. І. Pokhmurs’kyi,1 S. A. Kornii,1,2 and B. P. Kosarevych1
UDC 544.723.23: 620.193
We construct a cluster model of interaction of atomic hydrogen with α - and γ -iron surfaces and per-
form quantum-chemical computations of the Fe–H system by the method of density functional with the RPBE-GGA exchange-correlation functional. We obtain the curves of the potential energy of interaction of atomic hydrogen with iron clusters of BCC and FCC structures and establish the activation barriers of its adsorption, penetration into the subsurface layer, and migration between tetrahedral and octahedral positions of clusters. The energies of dissolution of atomic hydrogen at different absorption sites of the clusters are computed and the stable energy states of hydrogen in the octahedral positions of FCC iron clusters are revealed. We analyze the charge state of atomic hydrogen both on the surface and in the bulk sites of the clusters and confirm the mechanism of partial charge transfer in the iron–hydrogen system. Keywords: iron clusters, hydrogen, hydrogen absorption, method of density functional, octahedral and tetrahedral positions, charge of atomic hydrogen.
Since the beginning of the new century, the interest to the interaction of hydrogen with metals steadily increases [1–3]. The extensive development of investigations of metal–hydrogen systems is caused, on the one hand, by the practical importance of this problem, which currently occupies one of the leading places in the contemporary materials science in connection with the development of new radiation-resistant and hydride-forming materials for the nuclear and hydrogen power engineering and, on the other hand, by the harmful influence of hydrogen on the properties of materials (hydrogen embrittlement, corrosion, and crack propagation). Contemporary experimental methods of investigations and new theoretical approaches, including quantum-chemical calculations, substantially extend the level of understanding of the processes of interaction of hydrogen with metals. In particular, the notions of reconstruction of the surface in the course of chemisorption of hydrogen, its charge state on the surface and in the bulk of metals, migration of hydrogen in metals, etc. are developed in [4, 5]. Hydrogen atoms are characterized by a uniquely small mass and size as compared with the other interstitial atoms in metals and, therefore, exhibit high diffusion mobility. Despite the fact that hydrogen causes deformation of the metal (of dilatation character), the type of the crystal lattice often does not change even for high concentrations of hydrogen. Hence, the influence of hydrogen on the metal can be insignificant. Moreover, after hydrogenation, hydrogen can often be evacuated from the metal without degradation of properties of the metal. This opens the possibility of controlled action of hydrogen upon metals, i.e., of the hydrogen treatment of materials. On the other hand,
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