Heats of formation of Zirconium binary transition metal alloys

AbstractD-band model is used to predict enthalpies of formation of binary transition metal alloys. One of the input parameters of the model namely bandwidth is optimized by refinement procedures based on ab initio calculations and reliable calometric data for Zr-, Hf- and Ti-compounds. Revised values of enthalpies of formation ΔHfor for Zr-binary transition metal compounds using new values of bandwidth WZr∗=7.24eV are substantially improved. This improvement can be applied for other problematic cases in order to ameliorate results of ΔHfor calculated by d-band model

Simulations of a single membrane between two walls using a Monte Carlo method

Quantitative theory of interbilayer interactions is essential to interpret x-ray scattering data and to elucidate these interactions for biologically relevant systems. For this purpose Monte Carlo simulations have been performed to obtain pressure P and positional fluctuations sigma. A new method, called Fourier Monte-Carlo (FMC), that is based on a Fourier representation of the displacement field, is developed and its superiority over the standard method is demonstrated. The FMC method is applied to simulating a single membrane between two hard walls, which models a stack of lipid bilayer membranes with non-harmonic interactions. Finite size scaling is demonstrated and used to obtain accurate values for P and sigma in the limit of a large continuous membrane. The results are compared with perturbation theory approximations, and numerical differences are found in the non-harmonic case. Therefore, the FMC method, rather than the approximations, should be used for establishing the connection between model potentials and observable quantities, as well as for pure modeling purposes.Comment: 10 pages, 10 figure

A Simple Model of Liquid-liquid Phase Transitions

In recent years, a second fluid-fluid phase transition has been reported in several materials at pressures far above the usual liquid-gas phase transition. In this paper, we introduce a new model of this behavior based on the Lennard-Jones interaction with a modification to mimic the different kinds of short-range orientational order in complex materials. We have done Monte Carlo studies of this model that clearly demonstrate the existence of a second first-order fluid-fluid phase transition between high- and low-density liquid phases

Numerical investigation of geometrically nonlinear clamped uniform rods and rods with sections varying exponentially free vibration

Purpose: The present paper is intended to investigate the problem of linear and non-linear longitudinal free vibration of uniform rods and rods whose cross-sections vary exponentially at large vibration amplitudes. Design/methodology/approach: The method adopted consists in discretizing the energy term on linear kij and non-linear rigidity tensor bijkl, as well as the mass tensor mij. Therefore, the formulation of this structure is based on Lagrange equations and the harmonic balance method so as to obtain the nonlinear algebraic equations. These latter are solved numerically and analytically through the explicit and linearized method. Findings: The response of Clamped-Clamped uniform and non-uniform rods on our structure are highlighted in the amplitude frequency and associated first three mode shapes. Moreover, this research leads to study the influence of the exponential slope on the maximum displacement, thus emphasizing the non-uniform bars usefulness. The obtained results are then compared with the available literature with a view to validating this theory. Research limitations/implications: As a perspective, the method used in this paper would be pushed to study the FDM material, taking into account other parameters related to additive manufacturing, and later to be validated experimentally. Practical implications: Longitudinal vibrations are important in mechanical structures; therefore, the determination of their dynamic behaviour needs to be understood. In the present study, the effect of the displacement amplitude on the exponential slope of the structure was analysed, which led to the determination of the reduction range of the vibration amplitude under resonance. However, this should be taken into account in the design process. Besides, the usefulness of the non-linearity geometric effects was demonstrated to examine these structures by considering all the parameters involved. Originality/value: A linearized procedure is used to solve a nonlinear algebra equation. The use of this method leads to reduce calculation time contrary to iterative methods

Thermodynamic assessment of the calcium-germanium system

International audienceThermodynamic modeling of the Ca-Ge system was carried out by means of the CALPHAD (calculation of phase diagrams) method and new experimental phase diagram data The liquid phase and the intermetallic compounds Ca2Ge, Ca5Ge3, Ca7Ge6 (new compound), CaGe and CaGe2 are taken Into consideration in this optimization The substitutional solution model was used to describe the liquid phase. The five compounds were treated as stoichiometric phases A consistent set of thermodynamic parameters has been obtained. The optimized phase diagram and thermodynamic properties are presented and compared with other calculated and experimental data obtained from literatur

A study of the phase transitions, electronic structures and thermodynamic properties of Mg2X (X = Ge, Si and Sn) under high pressure

In this work, we theoretically investigate phase transitions, electronic structures and thermodynamic properties of Mg2X (X = Ge, Si and Sn) under high pressures. To reach this goal, the total energy has been calculated by using the full-potential linearized augmented plane wave (FP-LAPW) method with generalized gradient approximation (GGA), local density approximation (LDA) and Engel–Vosko approximation (EV-GGA), which are based on the exchange-correlation energy optimization. The fully relaxed structure parameters of Mg2X compounds are in good agreement with the available experimental data. Our results demonstrate that the Mg2X compounds undergo two pressure-induced phase transitions. The first one is from the cubic antifluorite (Fm3¯m) structure to the orthorhombic anticotunnite (Pnma) structure in the pressure range of 3.77–8.78 GPa (GGA) and 4.88–8.16 GPa (LDA). The second transition is from the orthorhombic anticotunnite structure to the hexagonal Ni2In-type (P63m¯mc) structure in the pressure range of 10.41–29.77 GPa (GGA) and 8.89–63.45 GPa (LDA). All the structural parameters of the high pressure phases are analyzed in detail. Only a small difference in the structural parameters is observed at high pressures between the calculated and experimental results. The electronic and thermodynamic properties are also analyzed and discussed. The establishment of the metallic state of the Mg2X (X = Ge, Si and Sn) compounds at high pressure is confirmed

Thermodynamic Modeling of the Al-Ba and Ba-Ge Systems Supported by First-Principles Calculations

WOS: 000466369300009The phase diagrams of Al-Ba and Ba-Ge systems are optimized by coupling the CALPHAD approach and first-principles calculations. The binary intermetallic compounds were treated as stoichiometric phases. The total energies of nine intermetallic compounds: Al4Ba, Al13Ba7, Al5Ba3, Al5Ba4, Ba2Ge, Ba5Ge3, BaGe, -Ba3Ge4 and BaGe2 were calculated by first-principles calculation using density functional theory approximation as implemented in the VASP (Vienna Ab-initio Simulation Package) code and used in the CALPHAD approach to assess the two systems. The liquid solutions are described by the Redlich-Kister polynomial model. A set of thermodynamic parameters were obtained for the Al-Ba and Ba-Ge systems. The calculated phase diagrams and thermodynamic properties are in good agreement with most of the accuracy available data