Analytical Bond-order Potential Research Articles

Parametrization protocol and refinement strategies for accurate and transferable analytic bond-order potentials: Application to Re

Parametrization protocol and refinement strategies for accurate and transferable analytic bond-order potentials: Application to Re

Atomistic modelling of the Pb-Bi system from a constructed bond order potential

Lead-bismuth eutectic (LBE) alloys are currently considered one of the most promising liquid metal coolants for fast reactors, and especially accelerator-driven systems (ADS). An analytical bond-order potential (BOP) of Pb-Bi has been constructed to account for the electronic interactions and angular contribution of Pb-Bi system. The newly developed BOP has been validated to show a better performance than the Pb-Bi potentials already published in the literature. Molecular dynamics simulations based on current BOP has been adopted to investigate various properties of Pb-Bi binary system. It accurately predict the heats of formation, density, and thermal expansion coefficient of liquid LBE at 700 K. The diffusion coefficient and viscosity of liquid Pb44.5Bi55.5 are calculated, which are in good agreement with experimental observations in the literature. These findings provide a foundation for future design of Pb-Bi eutectic alloys for use in ADS and heavy-metal-cooled fast nuclear reactors.

Vacancy segregation and intrinsic coordination defects at (1 1 1) twist grain boundaries in diamond

High radiation damage resistance has become increasingly important for applications of functional materials in harsh environments. The high radiation damage resistance diamond cubic carbon is a unique material which is considered for radiation environments. Beyond the intrinsic radiation hardness of crystal, the interaction between point defects and interfaces (e.g., grain boundaries) increases resistance to radiation damage. In effect, grain boundaries act as sinks for point defects and promote their mutual annihilation. Furthermore, interfaces can be exploited to obtain controlled segregation of point defects, thus avoiding the degradation of material properties due to uncontrolled point defect segregation and coalescence.In the present work, we investigate the interaction between vacancies – as a radiation defect in the bulk crystal – and (1 1 1) twist grain boundaries in crystalline diamond using atomistic simulation with analytical bond order potential. Based on previous observations on structure–property relationships characterising the (1 1 1) twist grain boundaries, this work analyses the emergence of periodic segregation patterns, which are rationalised by the underlying interface structure and their periodic intrinsic coordination defect populations. This observation suggests that randomly distributed vacancies in bulk single crystals can form self-organised defect arrays in the grain boundary. The coordination defect content correlates with the interface sink efficiency, providing guidelines for designing interfaces with high sink efficiency.

Developing an analytical bond-order potential for Hf/Nb/Ta/Zr/C system using machine learning global optimization

Despite being effective in unveiling the complicated nanostructure-property relation of (HfNbTaZr)C high-entropy carbide (HEC), applications of atomistic simulations are restricted by the lack of reliable many-body interatomic potentials. In this study, we propose a machine learning (ML) global optimization framework to parameterize an analytical bond-order potential (ABOP) with massive internal parameters for the Hf/Nb/Ta/Zr/C system. The combined distributed breeder genetic algorithm (DBGA), extensive ab initio training data and a normalized objective function markedly accelerate the convergence towards global optimum. By performing a cross-validation for the established potential, we demonstrate that the ABOP can accurately predict fundamental energetic, structural and mechanical properties of metals, intermetallic compounds, alloys and carbides in both the training and test datasets. Moreover, the potential is employed in dynamic simulations such as thermal annealing, simple loadings, nanoindentation and irradiation collision, from which some typical experimental observations are successfully reproduced. This not only further verifies the reliability of ABOP, but also implies its broad future applicability in nanoscale simulations.

Magnetic bond-order potential for iron-cobalt alloys

For large-scale atomistic simulations of magnetic materials, the interplay of atomic and magnetic degrees of freedom needs to be described with high computational efficiency. Here we present an analytic bond-order potential (BOP) for iron-cobalt, an interatomic potential based on a coarse-grained description of the electronic structure. We fitted BOP parameters to magnetic and non-magnetic density functional theory (DFT) calculations of Fe, Co, and Fe-Co bulk phases. Our BOP captures the electronic structure of magnetic and nonmagnetic Fe-Co phases. It provides accurate predictions of structural stability, elastic constants, phonons, point and planar defects, and structural transformations. It also reproduces the DFT-predicted sequence of stable ordered phases peculiar to Fe-Co and the stabilization of B2 against disordered phases by magnetism. Our Fe-Co BOP is suitable for atomistic simulations with thousands and millions of atoms.

Analytic bond order potential for indium gallium zinc oxide

Analytic bond order potential for InGaZnO4 compounds, allowing versatile investigation of their properties including dynamic formation via sputtering.

Diffusion and thermo-driven migration of silver, palladium, and ruthenium nanoparticles in cubic SiC matrix using molecular dynamics

The diffusion and thermo-driven migration behaviors of metal fission products in cubic SiC are critical for determining the safety of a high-temperature gas-cooled reactor, and the molecular dynamics (MD) approach can describe the phenomenon from a microscopic perspective. The interactions of three metal elements, Ag, Pd, Ru, and SiC, were described using the Analytical Bond-Order Potential (ABOP). The diffusion coefficient of metal nanoparticles within the SiC matrix was calculated at various temperatures, and the results revealed that Ag > Pd > Ru. Furthermore, thermo-driven migration simulations were carried out using three alternative matrix morphologies: pure cubic SiC, nano-polycrystalline SiC, and SiC with a nanochannel. It is illustrated that Ag nanoparticles transport farthest in the SiC nanocrack from the high-temperature region to the low-temperature region and the magnitude is considerably greater than that in the other two cases. Therefore, the size of the SiC nanochannel and metal nanoparticles were investigated additionally, indicating that there are optimal-matching geometric parameters for Ag and Ru, but no noticeable effect on Pd nanoparticles. The findings of this study allow for the calculation of the diffusion coefficient used in source term analysis, as well as the examination of fission product migration behavior in a large temperature gradient field.

Interatomic Potential for InP.

Classical modeling of structural phenomena occurring in InP crystal, for example plastic deformation caused by contact force, requires an interatomic interaction potential that correctly describes not only the elastic properties of indium phosphide but also the pressure-induced reversible phase transition B3↔B1. In this article, a new parametrization of the analytical bond-order potential has been developed for InP. The potential reproduces fundamental physical properties (lattice parameters, cohesive energy, stiffness coefficients) of the B3 and B1 phases in good agreement with first-principles calculations. The proposed interaction model describes the reversibility of the pressure-induced B3↔B1 phase transition as well as the formation of native point defects in the B3 phase.

Atomistic modelling of the immiscible Fe–Bi system from a constructed bond order potential

An analytical bond-order potential (BOP) of Fe–Bi has been constructed and has been validated to have a better performance than the Fe–Bi potentials already published in the literature. Molecular dynamics simulations based on this BOP has been then conducted to investigate the ground-state properties of Bi, structural stability of the Fe–Bi binary system, and the effect of Bi on mechanical properties of BCC Fe. It is found that the present BOP could accurately predict the ground-state A7 structure of Bi and its structural parameters, and that a uniform amorphous structure of Fe100−x Bi x could be formed when Bi is located in the composition range of 26 ⩽ x < 70. In addition, simulations also reveal that the addition of a very small percentage of Bi would cause a considerable decrease of tensile strength and critical strain of BCC Fe upon uniaxial tensile loading. The obtained results are in nice agreement with similar experimental observations in the literature.

Atomistic simulation of displacement damage and effective nonionizing energy loss in InAs

A molecular dynamics (MD) method, along with the analytical bond-order potential, is applied to study defect production in InAs. This potential is modified to obtain a better description for point-defect properties and is extended for proper applications in radiation damage simulation. By using this modified potential, the threshold displacement energy $({E}_{d})$, as one of the crucial parameters in radiation damage studies, is calculated over thousands of crystallographic directions for incorporating spatial anisotropy. However, the ${E}_{d}$ dependence on directions is found to be relatively weak. The defect production, clustering, and evolution in InAs are further investigated for the energies of the primary knock-on atom (PKA) ranging from 500 eV to 40 keV. A nonlinear defect production is seen with increasing PKA energy. This nonlinearity, which is associated with the direct-impact amorphization, is very distinctive for PKA energies ranging from 1 to 20 keV. Based on the damage density evaluated from molecular dynamics simulations, a theoretical model is developed for determining nonionizing energy loss (NIEL), which can be used for quantifying the electronic device degradation in a space radiation environment. The NIELs of InAs for proton, alpha, and Xe particles are calculated from the displacement threshold up to 60 MeV in comparison with available data so as to validate our model in the current study.

Исследование с помощью молекулярной динамики образования димеров на поверхности (001) GaAs при низких температурах

The simulation of dimers formation during the low-temperature reconstruction of GaAs (001) surface terminated with Ga or As atoms was performed by the molecular dynamics method using the analytical Bond-Order Potential based on quantum mechanical theory incorporating both σ- and π- bonds between atoms. A decrease in values of potential energy of the atoms during formation of isolated surface dimer have been determined. It has been found that potential energy of an atom in As-dimer is several tenths of an eV lower than in Ga-dimer. Kinetics of the initial stages of Ga-dimers formation in the temperature range of 25 - 40 K was studied. It was found that the characteristic thermal activation energy of single isolated Ga-dimers formation is ~ 29 meV, which is lower than the same value for As-dimers (~ 38 meV). Time constants characterizing the average rate of transformation of one dimer into a chain of two dimers at temperature range of 28 - 37 K were estimated. Inverse values of these parameters for paired Ga- and As-dimers are in the ranges of 10^11 – 10^12 s^-1 and 10^9 – 10^10 s^-1, respectively, while corresponding parameters for the formation of single dimers are in the ranges of 4·10^6 – 10^8 s^-1 and 1.4·10^6 – 7.4·10^7 s^-1.

Analytical bond-order potential for silver, palladium, ruthenium and iodine bulk diffusion in silicon carbide

The analytical bond-order potential has been developed for simulating fission product (Ag, Pd, Ru, and I) behavior in SiC, especially for their diffusion. We have proposed adding experimentally available elastic constants and physical properties of the elements as well as important defect formation energies calculated from density functional theory simulation to the list of typical properties as the extensive fitting database. The results from molecular dynamics simulations are in a reasonable agreement with defect properties and energy barriers of their experimental/computational counterparts. The successful validation of the new potential has established a good reliability and transferability of the potentials, which enables the ability of simulation in extended scale. The kinetic behavior such as diffusion of different interstitials is then realized by applying the new interatomic potentials. The bulk diffusion is less likely to dominate the transport of the four fission products under pure thermal condition, when we refer to their extremely small values of the effective diffusion coefficients. The interstitial mechanism is hard for Pd, Ru, and I to access due to the high formation energy and high migration energy. However, it is found that the migration energy of silver is relatively low, which indicates Ag diffusion via an interstitial mechanism being feasible, especially under irradiation condition, where massive interstitials can be formed in high-temperature nuclear reactors.

Molecular dynamics simulations of extended defects and their evolution in 3C–SiC by different potentials

An important issue in the technology of cubic SiC (3C–SiC) material for electronic device applications is to understand the behavior of extended defects such as partial dislocation complexes and stacking faults (SFs). Atomistic simulations using molecular dynamics (MD) are an efficient tool to tackle this issue for large systems at comparatively low computation cost. At this, proper choice of MD potential is imperative to ensure the reliability of the simulation predictions. In this work, we compare the evolution of extended defects in 3C–SiC obtained by MD simulations with Tersoff, analytical bond order, and Vashishta potentials. Key aspects of this evolution are considered including the dissociation of 60° perfect dislocations in pairs of 30° and 90° partials as well as the dependence of the partial dislocation velocity on the Burgers vector and the atomic composition of core. Tersoff potential has been found to be less appropriate in describing the dislocation behavior in 3C–SiC as compared to two other potentials, which in their turn provide qualitatively equivalent predictions. The Vashishta potential predicts much faster defect dynamics than the analytical bond order potential (ABOP). It can be applied therefore to describe the large-scale evolution of the dislocation systems and SFs. On the other hand, ABOP is more precise in predicting local atom arrangements and reconstructions of the dislocation core structures. In this respect, synergetic use of ABOP and Vashishta potential is suggested for the MD simulation study of the properties and evolution of extended defects in the 3C–SiC.

A computational study of the temperature dependence of interface and surface energies in WC–Co cemented carbides

Interfaces and surfaces often play a vital role for the properties of polycrystalline materials, such as cemented carbides, and the study of these planar defects is, therefore, of great importance. Cemented carbides (or hardmetals) is a unique class of materials where hard carbide (WC) grains, usually micrometer sized, are embedded in a more ductile metal binder phase (usually Co) in order to combine superb strength with high hardness, making them ideal as tool material in e.g. metal machining. In the manufacturing and industrial usage of cemented carbides temperatures reach high levels, especially in the former case where the material is sintered at temperatures where the binder phase is a liquid.This is a computational study of the temperature dependence of interface and surface energies in WC–Co cemented carbides upto and above the melting temperature of Co. We make use of an analytical bond order potential (ABOP) fitted to density functional theory (DFT) data in order to make the free energy calculations feasible. A variety of free energy methods are used: including quasi harmonic approximation, temperature and thermodynamic integration, and calculation of liquid surface tension and work of adhesion for phase boundaries. We present the temperature dependent interface and surface energies for some typical cases, data which should be useful as a supplement to other studies limited to 0 K.

Phase transitions in titanium with an analytic bond-order potential

Titanium is the base material for a number of technologically important alloys for energy conversion and structural applications. Atomic-scale studies of Ti-based metals employing first-principles methods, such as density functional theory, are limited to ensembles of a few hundred atoms. To perform large-scale and/or finite temperature simulations, computationally more efficient interatomic potentials are required. In this work, we coarse grain the tight-binding (TB) approximation to the electronic structure and develop an analytic bond-order potential (BOP) for Ti by fitting to the energies and forces of elementary deformations of simple structures. The BOP predicts the structural properties of the stable and defective phases of Ti with a quality comparable to previous TB parameterizations at a much lower computational cost. The predictive power of the model is demonstrated for simulations of martensitic transformations.

Physically\xa0informed artificial neural networks for atomistic modeling of materials

Large-scale atomistic computer simulations of materials heavily rely on interatomic potentials predicting the energy and Newtonian forces on atoms. Traditional interatomic potentials are based on physical intuition but contain few adjustable parameters and are usually not accurate. The emerging machine-learning (ML) potentials achieve highly accurate interpolation within a large DFT database but, being purely mathematical constructions, suffer from poor transferability to unknown structures. We propose a new approach that can drastically improve the transferability of ML potentials by informing them of the physical nature of interatomic bonding. This is achieved by combining a rather general physics-based model (analytical bond-order potential) with a neural-network regression. This approach, called the physically informed neural network (PINN) potential, is demonstrated by developing a general-purpose PINN potential for Al. We suggest that the development of physics-based ML potentials is the most effective way forward in the field of atomistic simulations.

Analytical interatomic bond-order potential for simulations of oxygen defects in iron

We present an analytical bond-order potential for the Fe–O system, capable of reproducing the basic properties of wüstite as well as the energetics of oxygen impurities in -iron. The potential predicts binding energies of various small oxygen-vacancy clusters in -iron in good agreement with density functional theory results, and is therefore suitable for simulations of oxygen-based defects in iron. We apply the potential in simulations of the stability and structure of Fe/FeO interfaces and FeO precipitates in iron, and observe that the shape of FeO precipitates can change due to formation of well-defined Fe/FeO interfaces. The interface with crystalline Fe also ensures that the precipitates never become fully amorphous, no matter how small they are.

A numerical study on subsurface quality and material removal during ultrasonic vibration assisted cutting of monocrystalline silicon by molecular dynamics simulation

Molecular dynamics (MD) simulation is used to study the subsurface quality and material removal of single crystal silicon with a diamond tool during ultrasonic elliptical vibration assisted cutting (UEVAC), 1D ultrasonic vibration assisted cutting (1D UVAC) and traditional cutting (TC) process. In the simulations, a long-range analytical bond order potential is used to describe the interaction inside the silicon specimen, providing a more accurate depiction of the atomic scale mechanisms of ductile plasticity, brittle fracture, and structural changes in silicon. The results show that UEVAC and 1D UVAC in cutting brittle material silicon causes a much smaller cutting force, much lower von Mises stress at the subsurface, larger material remove rate, lower compressive normal stress and and smaller shear stress In addition, the hydrostatic stress of subsurface for TC and 1D UVAC is much higher than that for UEVAC, which results in fewer Si-II and bct5-Si formed from the original Si-I in UEVAC. Moreover, the number of other atoms for UEVAC is overall smaller than those of using TC and 1D UVAC, which confirms that UEVAC produces a better subsurface. And atomic flow field analysis shows that the UEVAC tends to cut silicon in a more ductile mode. Besides, the temperature in front of tool edge and below the tool flank face of TC is much higher. This means that 1D UVAC and UEVAC have a positive effect on the tool life. However, the temperature in subsurface zone is overall larger, which reveals that 1D UVAC and UEVAC have a negative effect on the subsurface temperature.

Influence of elliptical vibration on the behavior of silicon during nanocutting

MDS (molecular dynamics simulation) was employed in this paper to study the nanometric cutting of monocrystalline silicon during the ultraprecision elliptical vibration–assisted cutting (UEVAC) process. The behavior of the workpiece during material removal by UEVAC has been studied, and the effects of different vibration frequencies, amplitude ratios, and phase differences on the deformation of the material have been carefully investigated. In these simulations, a long-range analytical bond order potential was used to model the interaction inside the silicon specimen. The results from the MDS showed that a smaller vibration frequency, higher amplitude ratio, or smaller phase difference generated less heat during cutting. Moreover, it was found that a smaller vibration frequency and a lower amplitude ratio lead to a larger material removal rate, and that a higher amplitude ratio could reduce the thickness of the subsurface damage and von Mises stress of the workpiece. However, the results showed that a smaller vibration frequency increased the overall magnitude of the resultant force. It was also found that the decrease of the amplitude ratios caused an increase in the average normal forces and the resultant forces. In addition, the use of a cutting amplitude ratio of 10/3 reduced the cutting force and tended to machine the workpiece in a more ductile mode due to there being less crack propagation. Besides, a phase difference of 120° improved the material removal rate, but a phase difference of 60° reduced the cutting force.

An Analytical Bond Order Potential for Mg-H Systems.

Magnesium-based materials provide some of the highest capacities for solid-state hydrogen storage. However, efforts to improve their performance rely on a comprehensive understanding of thermodynamic and kinetic limitations at various stages of (de)hydrogenation. Part of the complexity arises from the fact that unlike interstitial metal hydrides that retain the same crystal structures of the underlying metals, MgH2 and other magnesium-based hydrides typically undergo dehydrogenation reactions that are coupled to a structural phase transformation. As a first step towards enabling molecular dynamics studies of thermodynamics, kinetics, and (de)hydrogenation mechanisms of Mg-based solid-state hydrogen storage materials with changing crystal structures, we have developed an analytical bond order potential for Mg-H systems. We demonstrate that our potential accurately reproduces property trends of a variety of elemental and compound configurations with different coordinations, including small clusters and bulk lattices. More importantly, we show that our potential captures the relevant (de)hydrogenation chemical reactions 2H (gas)→H2 (gas) and 2H (gas)+Mg (hcp)→MgH2 (rutile) within molecular dynamics simulations. This verifies that our potential correctly prescribes the lowest Gibbs free energies to the equilibrium H2 and MgH2 phases as compared to other configurations. It also indicates that our molecular dynamics methods can directly reveal atomic processes of (de)hydrogenation of the Mg-H systems.