Monte Carlo Simulations of Surface Segregation in Cu Ni Alloys

1992 ◽  
Vol 291 ◽  
Author(s):  
A. Pasturel ◽  
V. Drchal ◽  
J. Kudrnovsky ◽  
P. Weinberger
Keyword(s):  
Experimental Data ◽  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Surface Segregation ◽  
Tight Binding ◽  
Electronic Structure Calculations ◽  
Orbital Method ◽  
Ni Alloys ◽  
Composition Profiles ◽  
Structure Calculations

ABSTRACTA new method coupling electronic structure calculations with Monte Carlo simulations has been developed to determine surface compositions in Cu-Ni alloys. The calculations are based on an effective Ising model with parameters as defined within the framework of the Generalized Perturbation Method (GPM) and as calculated by means of the tight-binding version of the linear muffin-tin orbital method. The composition profiles are obtained for the fcc(OOl) surface for three bulk compositions, namely Cu75Ni25, Cu50Ni50, and Cu25Ni75 and compared with available experimental data.

Surface Segregation Maps Derived from Tight-Binding Ising Model

2011 ◽  
Vol 172-174 ◽  
pp. 1008-1015 ◽  
Author(s):  
Jean Marc Roussel ◽  
Guy Tréglia ◽  
Bernard Legrand
Keyword(s):  
Experimental Data ◽  
Electronic Structure ◽  
Ising Model ◽  
Surface Energy ◽  
Surface Segregation ◽  
Tight Binding ◽  
Electronic Structure Calculations ◽  
Matrix Elements ◽  
Metal Element ◽  
Structure Calculations

Surface segregation in transition metals can be analysed within a generalised Ising model,derived from Tight-Binding electronic structure calculations, which identifies three driving forces:the difference in surface energy and atomic volume between the two components and their tendencyto order or phase separate in the bulk. Using this ”three effects” rule, we present here general mapswhich predict the tendency of the solute metal element to segregate (or not) at the surface of a metalmatrix, for the 702 solute/matrix systems that can be formed with transition metal elements. Ourpredictions compare fairly well to the existing ab initio calculations and experimental data availableon these systems. The few exceptions, which mainly concern given matrix elements are discussed indetails.

Kinetics of Surface Segregation in Metallic Alloys with First-Principles Interaction Parameters

1995 ◽  
Vol 398 ◽  
Author(s):  
L. T. Wille ◽  
S. Ouannasser ◽  
H. Dreyssé
Keyword(s):  
First Principles ◽  
Surface Segregation ◽  
Tight Binding ◽  
Surface Region ◽  
Electronic Structure Calculations ◽  
Segregation Behavior ◽  
Kinetics Of ◽  
Structure Calculations ◽  
Effective Cluster ◽  
Equilibrium Segregation

ABSTRACTWe report the results of Monte Carlo simulations of the kinetics of surface segregation at the (001) face of CuNi and MoW alloys. These two systems were selected because they are based on different lattice structures and show contrasting segregation behavior: CuNi exhibits a monotonie profile, while that of MoW is oscillatory. To describe the energetics we have determined a set of effective cluster interactions (ECI) which govern the ordering or clustering tendencies of these alloys. The ECI were obtained by means of tight-binding electronic structure calculations in which no adjustable or experimentally determined parameters were used. Equilibrium segregation profiles are calculated and a series of quenches are performed. The layer concentrations are studied as a function of time and the existence of metastable phases in the surface region is investigated.

ZERO AND FINITE TEMPERATURE STUDY OF SINGLE FULLERENE CAGES AND CARBON “ONIONS” — GEOMETRY AND SHAPE

1993 ◽  
Vol 07 (29n30) ◽  
pp. 1883-1895 ◽  
Author(s):  
A. MAITI ◽  
C.J. BRABEC ◽  
J. BERNHOLC
Keyword(s):  
Interatomic Potential ◽  
Critical Size ◽  
Tight Binding ◽  
Configurational Entropy ◽  
Electronic Structure Calculations ◽  
Carbon Onions ◽  
Three Body ◽  
Structure Calculations ◽  
Scaling Arguments

Scaling arguments are used to show that above a critical size of several thousand atoms, there is a stability crossover from single to multilayer cages. Conjugate gradient minimization using a classical three-body interatomic potential, as well as tight-binding electronic structure calculations yield ground-state configurations for large fullerene shells that are polyhedral with clearly faceted geometry. The structure, energetics and configurational entropy associated with low-energy defects are calculated and the number of defects estimated as a function of temperature. The role of these thermally generated defects on the shape of large fullerenes is investigated in order to explain the nearly spherical shapes of the newly discovered carbon “onions”.

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