Tight-binding potentials for transition metals and alloys (original) (raw)
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Model potential based on tight-binding total-energy calculations for transition-metal systems
Physical review, 1995
A semiempirical model potential to simulate properties of fcc transition metals is proposed. The attractive part of the potential has been obtained from a tight-binding Hamiltonian that takes into account the symmetry of the d orbitals and leads to a 2/3 power dependence on the effective coordination (or second moment of the local density of states) instead of the usual square-root dependence. The repulsive interaction is assumed to be of the Born-Mayer type. In order to use this potential for specific materials, four parameters are adjusted with experimental data. We present two different parametrizations and calculate bulk, defect, surface, and cluster properties comparing with experiment, ab initio calculations, and the usual second-moment approximation.
Melting properties of fcc metals using a tight-binding potential
Physical Review B, 1997
Using a constant-pressure Monte Carlo simulation we study the melting properties of fcc metals described by a second-moment tight-binding potential. We find good agrement with experimental melting temperature for lead ͑Pb͒ and a reasonable prediction for noble and transition metals. This was done by changing only an overall energy scale. The local structure of the metal below the melting point is distorted with respect to the perfect solid-phase structure. We associate the distortion with the appearance of defects in the crystalline phase which act as the precursor of the melting. The liquid has a considerable structure above the melting temperature which resembles the local structure of the solid. At higher temperatures where diffusional dynamics is activated the liquid loses its local structure. Our results suggest that the elastic instability alone cannot be responsible for the melting. ͓S0163-1829͑97͒00410-4͔
Development of n-body potentials for hcp–bcc and fcc–bcc binary transition metal systems
Computational Materials Science, 2008
Within the framework of the second-moment approximation of the tight-binding theory, n-body potentials are proposed for hcp, fcc and bcc transition metals and their alloys. Both the energies and their derivatives calculated from the proposed potentials go smoothly to zero at cutoff radii, thus avoiding the unphysical behaviors that may emerge in simulations. With the assistances of ab initio calculations, the proposed potentials are then applied to Zr, Hf, Cu, V, Nb, Ta and their binary alloys. It turns out that the n-body potentials can well predict the energy sequence of stable and metastable structures of these metals. The vacancy formation energies, surface energies and melting points derived from the potentials also match well with experimental results. Based on the constructed potentials, molecular dynamics simulations reveal that Cu-Nb and Zr-Nb metallic glasses could be formed within the composition range of about 15-72 and 8-80 at.% Nb, respectively, matching well with experimental observations. Voronoi analyses reveal that the dominating atomic packings in Cu-Nb metallic glasses are the icositetrahedron (CN = 14), icosihexahedron (CN = 15) and icosidihedron (CN = 13) with fractions of 33%, 26% and 21%, respectively.
Thermal and mechanical properties of some fcc transition metals
Physical Review B, 1999
The temperature dependence of thermodynamic and mechanical properties of six fcc transition metals ͑Ni, Cu, Ag, Au, Pt, Rh͒ are studied using molecular dynamics ͑MD͒ simulations. The structures are described at elevated temperatures by the force fields developed by Sutton and co-workers within the context of the tight binding approach. In these simulations the thermodynamic and mechanical properties are calculated in the temperature range between 0 to 1500 K using the statistical fluctuation expressions over the MD trajectories.
The quantum sutton-chen many-body potential for properties of fcc metals
1998
The simple Sutton-Chen Philos. Mag. Lett. 61, 139 (1990)] (SC) type many-body force eld leads to an accurate description of many properties of metals and their alloys. We h a ve modi ed SC to include quantum corrections (e.g., zero-point energy) in comparing properties to experiment, leading to the quantum Sutton-Chen, or Q-SC force eld. We have applied the Q-SC description to nine face-centered cubic (fcc) metals (Al, Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au). The Q-SC parameters were optimized to describe the lattice parameter, cohesive energy, b u l k m o d ulus, elastic constants, phonon dispersion, vacancy formation energy, a n d surface energy. These potentials were tested by calculating the equation of state, thermal expansion, and speci c heat. We nd generally good agreement with all properties, indicating that this Q-SC type force eld should be useful in molecular dynamics and Monte Carlo simulations of metallic alloys. To illustrate the application of these parameters, we show h o w they have been used for predicting the viscosity of liquid metal alloys, and alloy melting and solidi cation (to form crystal or glass).
A short range many-body potential for modelling bcc metals
Pramana, 1999
The problem considered is the fitting of a many-body interaction potential to bulk crystal data. A parameterisation of the potential is assumed which is based on physical considerations. The free parameters are determined by using global optimization to perform a least squares fit, to a large number of crystal properties. This has been achieved for body centered cubic (bcc) materials. The approach adopted here fits the bcc crystal structure, as the preferred minimum energy configuration for tungsten, and also fits the dimer energetics and the elastic properties of crystalline tungsten.
MATERIALS TRANSACTIONS, 2005
The thermodynamic properties of transition metals are studied by introducing face-centered cubic (FCC) lattice model. In order to treat actual systems as quantitatively as possible, empirical second moment approximation (SMA) potentials proposed by Rosato et al. and by Cleri et al., which have been used widely for molecular dynamics (MD) simulations, are employed. To overcome shortcomings of lattice-gas models such as neglecting internal entropy of the system, the potential is mapped onto FCC lattice using the renormalization technique. It is found that the computed linear thermal expansion coefficients agree well with the results of MD simulations.
Quantum-based atomistic simulation of materials properties in transition metals
Journal of Physics: Condensed Matter, 2002
We present an overview of recent work on quantum-based atomistic simulation of materials properties in transition metals performed in the Metals and Alloys Group at Lawrence Livermore National Laboratory. Central to much of this effort has been the development, from fundamental quantum mechanics, of robust many-body interatomic potentials for bcc transition metals via model generalized pseudopotential theory (MGPT), providing close linkage between ab initio electronic-structure calculations and large-scale static and dynamic atomistic simulations. In the case of tantalum (Ta), accurate MGPT potentials have been so obtained that are applicable to structural, thermodynamic, defect, and mechanical properties over wide ranges of pressure and temperature. Successful application areas discussed include structural phase stability, equation of state, melting, rapid resolidification, high-pressure elastic moduli, ideal shear strength, vacancy and self-interstitial formation and migration, grain-boundary atomic structure, and dislocation core structure and mobility. A number of the simulated properties allow detailed validation of the Ta potentials through comparisons with experiment and/or parallel electronic-structure calculations. Elastic and dislocation properties provide direct input into higher-length-scale multiscale simulations of plasticity and strength. Corresponding effort has also been initiated on the multiscale materials modelling of fracture and failure. Here large-scale atomistic simulations and novel real-time characterization techniques are being used to study void nucleation, growth, interaction, and coalescence in series-end fcc transition metals. We have so investigated the microscopic mechanisms of void nucleation in polycrystalline copper (Cu), and void growth in single-crystal and polycrystalline Cu, undergoing triaxial expansion at a large, constant strain rate-a process central to the initial phase of dynamic fracture. The influence of pre-existing microstructure on the void growth has been characterized both for nucleation and for growth, and these processes are found to be in agreement with the general features of void distributions observed in experiment. We have also examined some of the microscopic mechanisms of plasticity associated with void growth.
Lattice dynamics of FCC transition metals: A pseudopotential approach
Zeitschrift f�r Physik B Condensed Matter, 1990
Simple pseudopotential model for the binding energy of transition metals is proposed. The contribution of the s-like electrons is calculated in the second-order perturbation theory for the local model pseudopotential while that of the d-like electrons is taken into account by introduction of repulsive short-range interatomic potential. Model parameters were determined for ten fcc transitions metals (Cu, Ni, Fe, Co, Ag, Pd, Rh, Au, Pt, and Ir). This model was used for the calculation of the phonon dispersion and the density of states, as well as for the elastic constants and their pressure derivatives. Good agreement with experimental data was achieved for the overall shape of phonon spectra and even for the position of the Kohn anomalies in Pd and Pt. Existence of such anomalies is also stated for predicted phonon spectra of rhodium and iridium.