Incorporating charge transfer effects into a metallic empirical potential for accurate structure determination in (ZnMg)N nanoalloys

Low-energy configurations of Pt6Cu6 clusters and their physical-chemical characterization: a high-accuracy DFT study

Based on a combination of many-body potentials, an analysis of the inertia tensors and a Density Functional Theory framework, we use a method to harvest the lowest energy states of any set of cluster systems. Then, this methodology is applied to the Pt₆Cu₆ cluster case and the structural, chemical, electronic, anisotropy, magnetic and vibrational properties of the lowest energy isomers are studied. Unexpectedly, some tens of isomers with much lower energy than the precedent believed ground state [J. Chem. Phys., 131(4):044701] are found, which indicates the goodness of this methodology. Some of the isomers obtained present the point groups C_s, C_2v according to Schoenflies notation, while others do not exhibit specific symmetry operations. The global chemical descriptors as the ionization potential, the electron affinity and the chemical hardness have oscillating behaviors with overall decreasing trends as the energy of the isomer grows up, indicating a higher rate of deactivation by sintering processes and a higher strength of the adsorption of small molecules on these systems. We present interesting results of the electronic, magnetic, anisotropy, vibrational and thermal properties of these clusters and discuss them; what can be useful information for future experiments and technical applications in varied fields as catalysis, spintronics, molecular magnetism or magnetic storage information.

Why are Zn-rich Zn-Mg nanoalloys optimal protective coatings against corrosion? A first-principles study of the initial stages of the oxidation process

ZnMg alloys of certain compositions in the Zn-rich side of the phase diagram are particularly efficient, and widely used, as anticorrosive coatings, but a sound understanding of the physico-chemical properties behind such quality is still far from being achieved. The present work focuses on the first stage of the corrosion process, namely the initial growth of a sacrificial surface oxide layer, whose characteristics will condition the next stages of the corrosion. A comprehensive ab initio study, based on density functional theory, is carried out on ZnMg nanoalloys with 20 atoms and different compositions, which serve as model systems to simulate the complex processes that occur in extended granular surfaces. The structural and electronic properties, when progressive oxidation of the nanoalloys takes place, are analyzed in detail with the help of structural descriptors, energetic descriptors such as the oxygen adsorption energies and excess adsorption energies, as well as with electronic ones based on the topological analysis of the electron density and the electron localization function, from which a detailed analysis of the bonding patterns is extracted. We explain why small amounts of Mg create a very positive synergy between Zn and Mg that increases the reactivity to oxygen while reducing, at the same time, the stress induced on the cluster substrate, both facts working in favor of promoting the growth of the oxide crust whilst protecting the core. Moreover, we also show that stoichiometries close to the Mg₂Zn₁₁ and MgZn₂ compositions are the best candidates to optimize the protection against corrosion in Zn-Mg alloys, in agreement with the experimental observations.

Oxygen adsorption on (100) surfaces in Fe-Cr alloys

The adsorption of oxygen on bcc Fe–Cr(100) surfaces with two different alloy concentrations is studied using ab initio density functional calculations. Atomic-scale analysis of oxygen–surface interactions is indispensable for obtaining a comprehensive understanding of macroscopic surface oxidation processes. Up to two chromium atoms are inserted into the first two surface layers. Atomic geometries, energies and electronic properties are investigated. A hollow site is found to be the preferred adsorption site over bridge and on-top sites. Chromium atoms in the surface and subsurface layers are found to significantly affect the adsorption properties of neighbouring iron atoms. Seventy-one different adsorption geometries are studied, and the corresponding adsorption energies are calculated. Estimates for the main diffusion barriers from the hollow adsorption site are given. Whether the change in the oxygen affinity of iron atoms can be related to the chromium-induced charge transfer between the surface atoms is discussed. The possibility to utilize the presented theoretical results in related experimental research and in developing semiclassical potentials for simulating the oxidation of Fe–Cr alloys is addressed.