Cohesive Properties of Cu-X and Ni-X (In, Sn) Intermetallics: Ab Initio Systematics, Correlations and “Universality” Features

Abstract

This paper reports an analysis of the systematics of cohesive properties and equation-of-state parameters for a large number of stable, metastable and hypothetical binary MeaXb type phases formed by Me = Cu, Ni with X = In, Sn. To this aim, an ab initio database previously developed by the authors using spin polarized density-functional-theory calculations, using the VASP code, is adopted. The work involves the volume (V0), Wigner–Seitz radius, bulk modulus (B0) and cohesive energy (Ecoh) of the phases. At the outset of the paper it is shown that these properties can be studied as functions of the average group number (AGN), i.e., the weighted average of the number of valence electrons involved in the VASP calculations. Moreover, the cohesive energy density (CED), defined as Ecoh/V0, is shown to correlate very well with the AGN variable and with B0. These striking regularities are given two complementary interpretations. First, a general microscopic picture of the variations of cohesion is developed by studying the evolution of the contributions of the d- and p-electrons to their electronic density of states. In this way the effects of the hybridization of d- and p-electrons, and the filling up of bonding and anti-bonding states is highlighted. Next, a thermodynamic analysis based on the classical approach developed by Rose, Ferrante, Smith and collaborators is performed. It is concluded that the correlation involving CED and B0 is a manifestation of a significant degree of “universality” in the variation of the cohesive properties with the Wigner–Seitz radius of these compounds.