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José de San Martín, Argentina

Bonny G.,Belgian Institute for Nuclear Sciences | Pasianot R.C.,CAC CNEA | Pasianot R.C.,CONICET | Pasianot R.C.,Instituto Sabato
Philosophical Magazine Letters | Year: 2010

Many-body interatomic potentials play an important role in atomistic modelling of materials. For pure elements it is known that there exist gauge transformations that can change the form of the potential functions without modifying its properties. These same transformations, however, fail when applied to alloys. Even though different research groups may use the same potentials to describe pure elements, the gauges employed for fitting alloys will generally be different. In this scenario, it is a priori impossible to merge them into one potential describing the combined system, and thus no advantage is taken from state-of-the-art developments in the literature. Here, we generalise the gauge transformations applied to pure species in order to leave the properties of alloys invariant. Based on these transformations, a strategy to merge potentials developed within different gauges is presented, aiming at the description of the combined system. Advantage of existing state-of-the-art potentials is so taken, thus focusing the efforts on fitting only the missing interactions. Such a procedure constitutes a helpful tool for the development of potentials targeted to alloys of increased complexity, while maintaining the description quality of their constituents. © 2010 Taylor and Francis. Source


Bonny G.,Belgian Institute for Nuclear Sciences | Pasianot R.C.,CAC CNEA | Pasianot R.C.,CONICET | Terentyev D.,Belgian Institute for Nuclear Sciences | Malerba L.,Belgian Institute for Nuclear Sciences
Philosophical Magazine | Year: 2011

We present an Fe-Cr interatomic potential to model high-Cr ferritic alloys. The potential is fitted to thermodynamic and point-defect properties obtained from density functional theory (DFT) calculations and experiments. The developed potential is also benchmarked against other potentials available in literature. It shows particularly good agreement with the DFT obtained mixing enthalpy of the random alloy, the formation energy of intermetallics and experimental excess vibrational entropy and phase diagram. In addition, DFT calculated point-defect properties, both interstitial and substitutional, are well reproduced, as is the screw dislocation core structure. As a first validation of the potential, we study the precipitation hardening of Fe-Cr alloys via static simulations of the interaction between Cr precipitates and screw dislocations. It is concluded that the description of the dislocation core modification near a precipitate might have a significant influence on the interaction mechanisms observed in dynamic simulations. © 2011 Taylor & Francis. Source


Bonny G.,Belgian Institute for Nuclear Sciences | Pasianot R.C.,CAC CNEA | Pasianot R.C.,CONICET | Zhurkin E.E.,Saint Petersburg State University | Hou M.,Free University of Colombia
Computational Materials Science | Year: 2011

Prior to applying any interatomic potential, it is important to know the stability of the different phases it describes. In the literature many methods to determine the phase diagram from an interatomic potential are described. Although for pure elements the procedure to obtain the thermodynamic functions is well established, for alloys it is not. In this work a method is developed to determine the phase diagram, i.e., solubility limits and spinodal gap, for the case of miscibility gaps. The method combines Monte Carlo simulations in the isobaric semi-grand canonical ensemble, full thermodynamic integration and Redlich-Kister expansions to parameterize the Gibbs free energy. Besides numerical inaccuracies, this method does not rely on any physical approximations to determine the phase diagram of a given interatomic potential. The method is applied to two different Fe-Cr potentials that are widely used in the literature. The resulting phase diagrams are discussed by comparing them to the experimental one and ones obtained in other works from the same potentials. © 2011 Elsevier B.V. All rights reserved. Source


Di Napoli S.,CAC CNEA | Di Napoli S.,CONICET | Thiess A.,Julich Research Center | Blugel S.,Julich Research Center | Mokrousov Y.,Julich Research Center
Journal of Physics Condensed Matter | Year: 2014

Applying the generalization of the model for chain formation in break-junctions (Di Napoli et al 2012 J. Phys.: Condens. Matter 24 135501), we study the effect of light impurities on the energetics and elongation properties of Pt and Ir chains. Our model enables us to develop a tool ideal for detailed analysis of impurity-assisted chain formation, in which zigzag bonds play an important role. In particular we focus on H (s-like) and O (p-like) impurities and assume, for simplicity, that the presence of impurity atoms in experiments results in a ..M-X-M-X-... (M: metal, X: impurity) chain structure in between the metallic leads. Feeding our model with material-specific parameters from systematic full-potential first-principles calculations, we find that the presence of such impurities strongly affects the binding properties of the chains. We find that, while both types of impurities enhance the probability of chains being elongated, the s-like impurities lower the chain's stability. We also analyze the effect of magnetism and spin-orbit interaction on the growth properties of the chains. © 2014 IOP Publishing Ltd. Source


Di Napoli S.,CAC CNEA | Di Napoli S.,CONICET | Thiess A.,Julich Research Center | Blugel S.,Julich Research Center | Mokrousov Y.,Julich Research Center
Journal of Physics Condensed Matter | Year: 2012

In this work we present the generalization of the model for chain formation in break junctions, introduced by Thiess etal (2008 Nano Lett. 8 2144), to zigzag transition-metal chains with s and p impurities. We apply this extended model to study the producibility trends for noble-metal chains with impurities, often present in break junction experiments, namely, Cu, Ag and Au chains with H, C, O and N adatoms. Providing the material-specific parameters for our model from systematic full-potential linearized augmented plane-wave first-principles calculations, we find that the presence of such impurities crucially affects the binding properties of the noble-metal chains. We reveal that both the impurity-induced bond strengthening and the formation of zigzag bonds can lead to a significantly enhanced probability for chain formation in break junctions. © 2012 IOP Publishing Ltd. Source

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