Towards an understanding of the interaction of 4d elements in nickel using density functional theory

In this paper, the interaction energy of 4 d elements (Y… Cd) in a nickel matrix is calculated using density functional theory. Interactions from the first to fourth nearest-neighbour positions are considered, with a focus on first and second nearest neighbours. Nearest-neighbour interactions are strongly repulsive for elements with a low number of d electrons and are attractive for element combinations with an average number of 5 d electrons. The interaction energy correlates with the change in bond order and bond length and can in principle be explained by quantities that are calculated from the properties of isolated alloying elements in a nickel matrix. For the next-nearest neighbour interaction, the interaction is attractive for elements with a low number of d electrons and is in this case accompanied by a charge concentration between the elements. It is shown that, qualitatively, the interaction energy is related to the third moment of the density of states of the nickel atoms connecting the two alloying elements. Interactions of elements at greater distance are usually weak, but the third-nearest neighbour interaction energy can be related to that of the second-nearest neighbours.