Embedded Atom Method Interatomic Potential Research Articles

Modified embedded-atom method interatomic potentials for Mg–Al–Ca and Mg–Al–Zn ternary systems

Al, Ca, and Zn are representative commercial alloying elements for Mg alloys. To investigate the effects of these elements on the deformation and recrystallization behaviors of Mg alloys, we develop interatomic potentials for the Al–Ca, Al–Zn, Mg–Al–Ca and Mg–Al–Zn systems based on the second nearest-neighbor modified embedded-atom method formalism. The developed potentials describe structural, elastic, and thermodynamic properties of compounds and solutions of associated alloy systems in reasonable agreement with experimental data and higher-level calculations. The applicability of these potentials to the present investigation is confirmed by calculating the generalized stacking fault energy for various slip systems and the segregation energy on twin boundaries of the Mg–Al–Ca and Mg–Al–Zn alloys, accompanied with the thermal expansion coefficient and crystal structure maintenance of stable compounds in those alloys.

Second nearest-neighbor modified embedded atom method interatomic potentials for the Na unary and Na-Sn binary systems

Interatomic potentials for pure sodium and sodium-tin binary systems are developed on the basis of the second nearest-neighbor modified embedded-atom method (2NN MEAM) formalism. The potentials can describe various fundamental materials properties such as structural, elastic, thermodynamic, and thermal properties in reasonable agreements with experimental data and density functional theory (DFT) calculations. It is demonstrated that the potentials can be used for the development of sodium-tin-X ternary potentials and atomistic simulations to understand material phenomena and to search for tin-based alloy anode materials for sodium ion batteries.

Second nearest-neighbor modified embedded-atom method interatomic potentials for the Co-M (M = Ti, V) binary systems

Interatomic potentials for the Co–Ti and Co–V binary alloy systems have been developed based on the second nearest-neighbor modified embedded-atom method (2NN MEAM) interatomic potential formalism. Newly developed potentials reproduce various structural and thermodynamic properties of the binary alloys in reasonable agreement with experiments, first-principles calculations, and CALPHAD-type thermodynamic assessments. It is emphasized that these potentials can serve as groundwork for atomistic studies on the design of highly efficient trimetallic noble metal catalysts.

Second-nearest-neighbor modified embedded-atom method interatomic potential for Cu-M (M = Co, Mo) binary systems

Second-nearest-neighbor modified embedded-atom method (2NN MEAM) interatomic potentials for Cu-M (M = Co, Mo) binary systems have been developed. The Cu-M potentials can be extended to Pt-Cu-M ternary 2NN MEAM potentials being combined with already existing Pt-M potentials and can be utilized for atomistic simulations to design inexpensive and efficient platinum alloy catalysts. The potentials reproduce fundamental material properties such as structural and thermodynamic properties of compound and solution phases in reasonable agreement with experimental data. Herein, the validity of the developed potentials for atomistic simulation is ascertained.

Structural changes and kinetics of shear banding in metallic glass composites

In this work we studied the mechanical behavior, structural changes and kinetics of shear banding during compression tests of Cu–Zr-based metallic glass composites using molecular dynamics simulations. Starting from a Cu45Zr45Al10 metallic glass model, two composite models were generated by adding 2% in volume of CuZr (B2 structure) nanocrystals of 4 and 17 nm in diameter, respectively. The three models were then deformed in compression using embedded-atom method (EAM) interatomic potentials. Local shear strain analyses showed that the kinetics of shear banding could be modeled as a two-stage process: 1) shear band formation due to the coalescence of shear transformation zones, and 2) shear band coarsening/thickening. The growth rate of the first stage (coalescence of shear transformation zones) varied upon the addition of CuZr nanocrystals, while the growth rate of the second stage remained unchanged. The addition of CuZr nanocrystals did not induce significant changes in the radial distribution function and distribution of Voronoi polyhedra of the glassy matrix, independently of the nanocrystal size. However, the addition of CuZr nanocrystals induced changes in the rate at which the local density of Cu-centered ⟨0,0,12,0,0⟩ icosahedra decreased with strain (“kinetics of icosahedra destruction”). These changes in local density were also modeled as a two-stage process with corresponding growth rates very similar to those obtained for the kinetics of shear banding, thus indicating a close relationship between the kinetics of icosahedra destruction and the kinetics of shear banding.

An embedded-atom method potential parameterized for sulfur-induced embrittlement of nickel

The embrittling or strengthening effect of solute atoms at grain boundaries (GBs), commonly known as the embrittling potency, is an essential thermodynamic property for characterizing the effects of solute segregation on GB fracture. One of the more technologically relevant material systems related to embrittlement is the Ni–S system where S has a deleterious effect on fracture behavior in polycrystalline Ni. In this work, we develop a Ni–S embedded-atom method (EAM) interatomic potential that accounts for the embrittling behavior of S at Ni GBs. Results using this new interatomic potential are then compared to previous density functional theory studies and a reactive force-field potential via a layer-by-layer segregation analysis. Our potential shows strong agreement with existing literature and performs well in predicting properties that are not included in the fitting database. Finally, we calculate embrittling potencies and segregation energies for six [100] symmetric-tilt GBs using the new EAM potential. We observe that embrittling potency is dependent on GB structure, indicating that specific GBs are more susceptible to sulfur-induced embrittlement.

Size effect in molecular dynamics simulation of nucleation process during solidification of pure metals: investigating modified embedded atom method interatomic potentials

Due to the significant increase in computing power in recent years, the simulation size of atomistic methods for studying the nucleation process during solidification has been gradually increased, even to billion atom simulations (sub-micron length scale). But the question is how big of a model is required for size-independent and accurate simulations of the nucleation process during solidification? In this work, molecular dynamics simulations with model sizes ranging from ∼2000 to ∼8 million atoms were used to study nucleation during solidification. To draw general conclusions independent of crystal structures, the most advanced second nearest-neighbor modified embedded atom method interatomic potentials for Al (face-centered cubic), Fe (body-centered cubic), and Mg (hexagonal-close packed) were utilized for molecular dynamics simulations. We have analyzed several quantitative characteristics such as nucleation time, density of nuclei, nucleation rate, self-diffusion coefficient, and change in free energy during solidification. The results showed that by increasing the model size to about two million atoms, the simulations and measurable quantities become entirely independent of simulation cell size. The prediction of cell size required for size-independent computed data can considerably reduce the computational costs of atomistic simulations and at the same time increase the accuracy and reliability of the computational data.

Modified embedded-atom method interatomic potential for the Mg–Zn–Ca ternary system

Mg–Zn–Ca alloys are representative Mg alloys with high formability at room temperature. Their high formability is thought to be related to slip, twinning, and recrystallization of the alloys, but the detailed mechanisms have not yet been clarified. To enable atomistic simulations for investigating those behaviors, an interatomic potential for the Mg–Zn–Ca ternary system was developed. The development was based on the second nearest-neighbor modified embedded-atom method formalism, combining previously developed Mg–Zn and Mg–Ca potentials with the newly developed Zn–Ca binary potential. The Zn–Ca and Mg–Zn–Ca potentials reproduce structural, elastic, and thermodynamic properties of compounds and solution phases of relevant alloy systems in reasonable agreement with experimental data, first-principles and CALPHAD calculations. The applicability of the developed potentials is demonstrated through calculations of the effects of Zn and Ca solutes on the generalized stacking fault energy for various slip systems, segregation energy on twin boundaries, and volumetric misfit strain.

A systematic study on the MEAM interatomic potentials of the transition metal nitrides TMNs (TM=Ti, V, Cr, Fe) binary systems

The second nearest-neighbor modified embedded-atom method (2NN MEAM) interatomic potentials for the transition metal nitrides TMNs (TM = Ti, V, Cr, Fe) binary systems have been developed according to a new regulation. The obtained potentials can excellently reproduce the structural and thermodynamic properties of the TMNs. Furthermore, the molecular dynamics (MD) uniaxial tension simulations for these binary systems indicate that the newly developed potential parameters can be applied successfully to investigate atomic-scale mechanisms underlying the response of TMNs to external stimuli (e.g. temperature, pressure etc.).

Embedded-atom method interatomic potential for boron nanostructures

Parameters of embedded-atom method interatomic potential for boron are presented in this paper. The potential parameters were determined by means of ab initio data for boron cluster B20, triangular boron sheet, and body-centered cubic structure. The potential has been tested against basic properties of various boron structures. They are face-centered cubic, diamond-like, body-centered tetragonal, icosahedron B12 and icosahedral chain structures. One can conclude that the proposed potential provides a reasonable representation of the interatomic interaction in boron nanostructures, and it is intended for use in large-scale molecular dynamics simulations of boron nanomaterials.

Plane and plane-radial discrete breathers in fcc metals

Discrete breather (DB) is a time-periodic, spatially localized vibrational mode in a perfect nonlinear lattice. In this study, two new types of DBs are reported in fcc metals (Al, Cu and Ni), based on the molecular dynamics simulations using standard embedded atom method interatomic potentials. All calculations are performed at a zero temperature in a three-dimensional computational cell with the use of periodic boundary conditions. A plane DB is excited in a single (111) atomic plane by displacing the atoms from their equilibrium lattice sites according to a specific pattern corresponding to a delocalized vibrational mode in a two-dimensional triangular lattice. This plane DB is delocalized in two dimensions and localized in one dimension, normal to the excited (111) plane. It is shown that in all studied metals the plane DBs have maximal lifetimes of 17–22 ps in the range of initial amplitudes of 0.15–0.30 Å. Herewith the studied mode demonstrates a hard type of nonlinearity, i.e. its frequency increases with amplitude. The second new type of DB is the plane-radial DB obtained by imposing a radial localizing function on the plane DB. This disk-type DB is localized in all three dimensions. The time evolution of the atomic displacement amplitudes and the kinetic energy are studied. The DBs of this type can exist for 9 and 4 ps in Cu and Ni, respectively, and then they decay by dissipating their vibrational energy onto neighboring atoms. The long-lived plane-radial DB in Al is not found.

Analysis of plastic strain-enhanced diffusivity in nanocrystalline iron by atomistic simulation

Plastic deformation may affect bulk diffusion in nanocrystalline materials by altering the rates of point defect production and annihilation. In the present work, a detailed analysis of this phenomenon is given by a series of molecular dynamics (MD) simulations to clarify the effect of preplastic strain on the diffusivity of iron atoms. The embedded atom method interatomic potential was used to perform MD simulations. The self-diffusion coefficient of iron atoms in unstrained and prestrained samples was measured over temperatures ranging from 600 to 1000 K and at total strains of 5%–20%. The results reveal that the diffusivity is indeed enhanced as a result of plastic straining, especially at low temperatures. The calculated diffusion coefficient of iron atoms in the prestrained samples is 10–80 times higher than that in the unstrained samples. The atomic structure analysis results indicated that the generation of excess vacancies and unstructured region by preplastic deformation contributes to the enhancement of self-diffusion under plastic straining conditions. At low temperatures, preplastic straining has a considerable effect in the peak shifting and broadening of the radial distribution function, which probably lowers the activation barrier height for diffusion.

Electrical resistivity of liquid expanded metals by Ziman approach

Transport properties of metals near the critical points were intensively studied. Using quantum dynamics simulations, we consider the structures of liquid aluminum and copper at high equilibrium temperatures and strong expansion. On the other hand, we carry out classical molecular dynamics simulations using the embedded atom method interatomic potentials. Both approaches provide data for resistivity calculations based on the well-known Ziman–Evans formula. The results of these calculations show a weak dependence on the used methods of ion structure computations. Also, we demonstrate that an effect of electron exchange and correlation is taken into account in electron–ion screening function, makes electric resistivity smaller in all considered situations.

Atomic Scale Study on the Tension-Compression Asymmetry of Single Crystalline and Nanocrystalline NiTi Shape Memory Alloy

The tension-compression asymmetry of single crystalline and nanocrystalline NiTi shape memory alloys (SMAs) is investigated at atomic scale utilizing molecular dynamics (MD) simulation. This study is based on the second nearest neighbor modified embedded-atom method interatomic potential for Ni-Ti binary systems. First of all, multiple variants of martensite are simulated via temperature-induced martensitic transformation in single crystal and nanocrystalline. The characteristics of forward and reverse martensitic transformation is derived by means of the atomic structural evolution. Secondly, it is observed that the tension-compression asymmetry for single crystalline NiTi is attributed to types of stress induced martensitic variants and martensitic reorientation, which respectively leads to stress asymmetry and strain asymmetry. However, the phenomenological tension-compression asymmetry in nanocrystalline is mainly credited to stress-induced martensitic variants, no obvious martensitic reorientation occurs under tension and compression loads. The corresponding atomic-scale structural evolution also explains why the length of tensile stress plateau in nanocrystalline is shorter than that of the single crystal. Finally, the nanocrystalline tension-compression asymmetric behavior is simulated under a broad range of temperature to obtain the critical stress-temperature relation. The simulation results are compared with the corresponding results obtained by experiment reported in the literature. The tension-compression asymmetry mechanism of single crystalline and nanocrystalline NiTi shape memory alloy is derived based on numerical results at atomic scale.

Modified embedded-atom method interatomic potential for Mg–Y alloys

An interatomic potential for the Mg–Y binary system is developed within the framework of the second-nearest-neighbor modified embedded-atom method (MEAM) based on a very good MEAM potential for pure Mg. The Mg–Y potential is fitted to a range of key physical properties, either experimental or computed by first-principles methods, including the Y interaction energy with basal and pyramidal stacking faults, and properties of the B2 Mg–Y intermetallic phase. Reasonable agreement is obtained—much better than existing potentials in the literature—but differences remain for subtle but important aspects of Y solutes in Mg. The predictions of the potential for Y misfit volume in Mg, Y solute interactions with the pyramidal II edge dislocation and tension-twin boundary are then compared against recent density functional theory results, and reasonable accuracy is obtained. In light of the spectrum of results presented here, the applicability and limitations of this Mg–Y MEAM potential for investigating various plasticity phenomena in Mg–Y solid solution alloys are carefully discussed.

Second nearest-neighbor modified embedded-atom method interatomic potentials for the Pd-M (M = Al, Co, Cu, Fe, Mo, Ni, Ti) binary systems

Palladium (Pd) has attracted attention as one of the major components of noble metal catalysts due to its excellent reactivity to a wide range of catalytic reactions. It is important to predict and control the atomic arrangement in catalysts because their properties are known to be affected by it. Therefore, to enable atomistic simulations for investigating the atomic scale structural evolution, we have developed interatomic potentials for Pd-M (M = Al, Co, Cu, Fe, Mo, Ni, Ti) binary systems based on the second nearest-neighbor modified embedded-atom method formalism. These potentials reproduce various fundamental properties of the alloys (the structural, elastic and thermodynamic properties of compound and solution phases, and order-disorder transition temperature) in reasonable agreements with experimental data, first-principles calculations and CALPHAD assessments. Herein, we propose that these potentials can be applied to the design of robust bimetallic catalysts by predicting the shape and atomic arrangement of Pd bimetallic nanoparticles.

Effects of the short-range repulsive potential on cascade damage in iron

Recent work has shown that the repulsive part of the interatomic potential at intermediate atomic separations strongly affects the extent and morphology of the damage produced by collision cascades in molecular dynamics simulations. Here, we modify an existing embedded atom method interatomic potential for iron to more accurately reproduce the threshold displacement energy surface as well as the many-body repulsion at intermediate and short interatomic distances. Using the modified potential, we explore the effects of an improved repulsive potential on the primary damage production and the cumulative damage accumulation in iron. We find that the extent of the damage produced by single cascades, in terms of surviving Frenkel pairs, directly correlates with the change in threshold displacement energies. On the other hand, the damage evolution at higher doses is more dependent on the formation and stability of different defect clusters, defined by the near-equilibrium part of the interatomic potential.

Atomistic simulation of shape memory effect (SME) and superelasticity (SE) in nano-porous NiTi shape memory alloy (SMA)

Porosity can play an important role in altering the phase transformation characteristics of NiTi shape memory alloys (SMA), thus changing its shape memory as well as its superelasticity properties. This work, based on atomistic simulations of binary NiTi SMA, documents the effects of porosity at the nanometer length scale on phase fraction evolution kinetics, transformation temperatures, and stress-strain response. Classical molecular dynamics simulations are performed using a well-examined and verified Finnis-Sinclair type embedded-atom method interatomic potential. Simulation results for the nano-porous NiTi with various porosity configurations are compared to non-porous NiTi. The martensite phase fraction and transformation temperatures increase noticeably with increasing porosity, and the stress-strain response shows noticeable variation with porosity. The residual strain and hysteretic energy dissipation capacity increase significantly with increasing porosity.

Connecting interatomic potential characteristics with deformation response in FCC materials

We present a molecular dynamics study using six different FCC model embedded atom method interatomic potentials. We investigate the relationship between specific interatomic force law properties and the deformation response of nano-scale grain boundary networks. We used a fully periodic quasi three-dimensional sample with random [1 1 0] tilt boundaries, adjusted for the lattice parameter of each potential. This procedure enabled the study of deformation behavior differences to be attributed to the potential used. The interatomic potential characteristics of cohesive energy, elastic constants and stable and unstable stacking fault energies were correlated with grain boundary structure and energy, the yield and flow stress, and the contributions to plasticity from dislocation emission and grain boundary sliding. We find non-planar features in the grain boundary structure for interatomic potentials characterized by low stacking fault energy. In turn, these non-planar features in the grain boundary hinder grain boundary sliding deformation mechanisms. Dislocation emission from the grain boundaries is controlled by the unstable stacking fault energy. The overall yield and flow stresses observed for these nano-scale grain boundary networks correlate with the unstable stacking fault energy given by the potential.

Critical assessment of Pt surface energy – An atomistic study

Despite the fact that surface energy is a fundamental quantity in understanding surface structure of nanoparticle, the results of experimental measurements and theoretical calculations for the surface energy of pure Pt show a wide range of scattering. It is necessary to further ensure the surface energy of Pt to find the equilibrium shape and atomic configuration in Pt bimetallic nanoparticles accurately. In this article, we critically assess and optimize the Pt surface energy using a semi-empirical atomistic approach based on the second nearest-neighbor modified embedded-atom method interatomic potential. That is, the interatomic potential of pure Pt was adjusted in a way that the surface segregation tendency in a wide range of Pt binary alloys is reproduced in accordance with experimental information. The final optimized Pt surface energy (mJ/m2) is 2036 for (100) surface, 2106 for (110) surface, and 1502 for (111) surface. The potential can be utilized to find the equilibrium shape and atomic configuration of Pt bimetallic nanoparticles more accurately.