•A new formalism of the n-body interatomic potentials is developed by explicitly accounting for 3-body interactions.•The interatomic potentials for V are constructed.•The formalism more accurately ...predicts properties of V in comparison with the available potentials.
An improved accuracy in the description of base characteristics of the bcc refractory metals, including melting point and heat of fusion, with the help of atomistic simulation methods, requires further development of reliable interatomic potentials, more precisely taking into account the angle part of interactions. A new approach for the description of interactions in atomistic systems based on known n-body expansion of the total energy has been developed. The embedded atom method (EAM) ansatz is derived from this expansion within a centrally symmetric approximation. With the developed approach, the total energy is regarded consisting of a pair potential part, 3-body interactions without model considerations and a term that describes all other n-body interactions like the embedded function of EAM. As an application, accurate many-body potentials for V have been constructed. The formation energies and volumes of self-interstitials and di-vacancies are calculated. The cohesive energy, elastic constants, phonon spectra, the vacancy formation and migration energies, surface energies, the transition to a rhombohedral phase with increasing pressure, the thermal expansion, the melting point and the heat of fusion have also been studied, and satisfactory agreement with available experimental data has been found.
In this work, the results of the evolutionary variable-composition search for binary compounds in the Ti–Si system are presented. The evolutionary algorithm did not find any new stable structures of ...silicides at 0 K and 0GPa. On the other hand, many low-energy metastable and unstable structures are predicted. The 33 predicted and 10 known from literature but previously unstudied structures of compounds with low formation energies with respect to the ground-state line are analyzed. The mechanical properties, electronic band structures, densities of states, and temperature dependencies of thermodynamic stability of 17 dynamically stable previously unstudied structures are calculated.
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The development of low-swelling radiation-resistant alloys is vital for the creation of reliable fusion reactors. In this article, we revisit the long-standing problem of very low radiation swelling ...in V-Ti-Cr alloys by means of DFT calculations. In particular, we study double and triple interactions of point defects such as solutes, vacancies and self-interstitial atoms in bcc V. According to our results titanium atom and vacancy are strongly attracted and in addition to pairs form highly stable triple Ti-Vacancy-Ti complexes, which are absent in the case of chromium. By using an analytic model of void growth and using calculated binding energies of point defect complexes in bcc vanadium we obtain three orders of magnitude reduction of swelling rate due to the formation of Ti-Vacancy-Ti complexes, which allows to explain experimental observations. Finally, we explain the causes of the strong attraction between titanium and vacancy using geometry and electronic structure analysis.
In this work, the interatomic potentials for modeling diffusion in the C15 Cr2Ta Laves phase were constructed within the N-body approach. The potential for Ta–Ta interactions reproduces the lattice ...parameter, cohesive energy, elastic constants, equation of state, thermal expansion, point defect energies, and phonon dispersion of body-centered cubic Ta in qualitative agreement with density functional theory (DFT) data and almost quantitative agreement with available experimental data in the temperature range of stability of C15 Cr2Ta Laves phase. The potential for Cr–Ta interactions reproduces the elastic constants, point defect properties, equilibrium volumes, and formation enthalpies of Cr–Ta structures in qualitative agreement with DFT data. Also, it reproduces the lattice stability and high-temperature formation enthalpy of C15 Cr2Ta Laves phase in very close agreement with the available experimental data. The calculations of diffusion coefficients with constructed potentials showed that diffusion in C15 Cr2Ta lattice is governed by Cr atoms which cannot move without creation of vacancies. The constructed potentials can be used in further investigations of diffusion processes in Cr–Ta phases at temperatures up to 2000 K, while the obtained results on diffusion coefficients in C15 Cr2Ta Laves phase would be useful in the rational design of Cr–Ta based alloys.
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In this paper, we evaluated the influence of vibrational and electronic free energy on the thermodynamic phase stability of the Ti5Si3, Ti3Si, Ti6Si3, and other silicides in the binary Ti-Si system ...and the solubility of Si in α-Ti within the density functional theory and harmonic approximation. We showed, that vibrational and electronic free energy thermodynamically stabilize the Ti3Si silicide and destabilize the Ti6Si3 silicide with respect to the Ti5Si3 and α-Ti. According to our calculations, the transition from equilibrium of Si solid solution with the Ti5Si3 silicide to the equilibrium of Si solid solution with the Ti3Si silicide should be at ∼ 900 K. The account of both the vibrational and electronic free energy increase the calculated solubility limit of Si in α-Ti and make it closer to the experimental one.
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•Vibrational free energies of hydrogen solid solution and titanium hydrides are calculated.•Solubility of hydrogen in titanium is predicted.•The influence of hydrogen on concentration ...of H-vacancy complexes is estimated.
The saturation solubility of hydrogen with respect to titanium hydrides, and the concentration of H-vacancy complexes in α-Ti are predicted on the basis of a thermodynamic model and ab initio calculated free energies. The presence of hydrogen increases the vacancy complex concentration by several orders of magnitude, with most of these complexes containing three H atoms. We show also that the solubility of hydrogen within the titanium is strongly influenced by the temperature-dependent free energy terms, and that by including these terms in the thermodynamic model it is possible to obtain good agreement with experiment.
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•The Fe-Fe complexes increase Fe solubility in hcp Ti.•The Fe atoms strongly segregate at grain boundaries in hcp Ti.•The Fe segregation can stabilize nanostructured titanium alloys.
...Iron is a potential element for developing cheap titanium alloys and a possible stabilizer of the nanostructured state. In this work, solubility, formation of Fe-Fe complexes and grain boundary segregation of Fe are studied in α-titanium using density functional theory. It is found that Fe prefers to be in substitutional sites in the bulk region and in interstitial sites at grain boundaries of α-Ti. The main contribution to solubility is provided by strongly bound Fe-Fe complexes. At certain conditions segregation of iron can provide notable stabilization of grain boundaries, reducing their energy by more than 200mJ/m2. Finally, it is shown that precipitation of Fe at Ti grain boundary is a favorable process that occurred without nucleation barriers.
In molecular dynamics simulations, there are dozens of potentials of different type, which take into account the angular dependence of the potential energy, for describing the interactions in carbon. ...Each of them describes simultaneously only a part of its physical properties. Meanwhile, a recently developed N-body approach provides the ability to set the required precision of this angular dependence. In particular, in this work we will show how accuracy in describing three-body interactions influences the accuracy of reproduction of physical properties of carbon on the example of one and two basis functions for these interactions. For both potentials, the identical optimization procedure, including fitting database and weights of each target value, was performed. We found that the last one reproduces the structural, elastic and defect properties of diamond, graphite and graphene phases of carbon in better agreement with experimental and theoretical data than the potential with only one basis function. For additional benchmark of this potential we assessed the melting point of graphite, which is predicted in an acceptable agreement with the experimental value.
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•A new interatomic potential for carbon was developed.•An increase of basis functions improves the description of carbon structures.•The potential with one functions predicts graphite structures as unstable.•The potential with two functions predicts three main carbon structures as stable.
We present a new interatomic potential for atomistic modeling of α- and β-phases of zirconium. The potential was developed within the framework of the N-body approach, which takes into account pair, ...three-body and many-body interactions. The new potential predicts a wide range of zirconium properties in agreement with known experimental and DFT data including structural energies, elastic constants, energies of point and planar defects, thermodynamic properties, such as melting temperature and α−β transition temperature. The potential predicts the mechanical instability of the β-phase of zirconium at 0 K, as well as relaxation effects of internal degrees of freedom in elastic constants. The predicted interstitial stacking fault energy is in a good agreement with the DFT data. The formation energies of self-interstitial atoms in the α-phase are in agreement with the known DFT values, predicting the basal octahedral (BO) configuration as the most stable. The potential predicts a spontaneous β−α transition with decreasing temperature. The calculated α−β phase transition temperature is 20% higher than the experimental value. The potential accurately predicts the melting temperature of zirconium, due to which a good agreement with the experimental data was obtained on the temperature dependencies of the diffusion coefficients for the α- and β-phases of zirconium. For both phases, the main contribution to the diffusivity is due to vacancies, while the corresponding values for interstitials are by one or two orders of magnitude lower. The potential predicts the deviation from the Arrhenius law of the temperature dependence of the diffusion coefficient for the β-phase of zirconium, due to the nonlinear dependence of the Gibbs energy of a vacancy formation on temperature. The constructed potential can be used for molecular dynamics simulations of α- and β-phases of zirconium and further development of interatomic potentials within the framework of the N-body approach for alloys containing zirconium.
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•A new interatomic potential for zirconium was developed.•The new potential accurately predicts defect and thermal properties of Zr.•The new potential predicts the spontaneous phase transition β–α.•Diffusivity in α and β phases of Zr is in agreement with the experimental data.
Tungsten, as the most refractory metal, is applied in fusion reactor in parts subjected to high temperatures and strong neutron irradiation. These factors lead to intense diffusion processes causing ...degradation of the material. Experimental investigations under such conditions are usually highly complicated and cannot provide a comprehensive understanding of the occurring phenomena. Therefore, their combination with theoretical approaches is required. One of the most robust approaches to simulate diffusion processes is molecular dynamics simulations based on classical interatomic potentials. It allows modeling relatively large samples consisting of several grains, grain boundaries, dislocations, and other types of defects for a reasonable computational time. The reliable simulations of the diffusion process require interatomic potentials satisfying the following criteria: prediction of melting point and thermal expansion as close as possible to the experimental values because the diffusion coefficient strongly depends on the homologous temperature and size factor. In the present paper, we present the new interatomic potential for tungsten, developed within the N-body approach, which reproduces the experimental value of melting temperature (3695 K) and thermal expansion at temperatures up to a melting point. The calculated diffusion coefficient demonstrates adequate agreement with experimental results. The constructed potential is applicable for simulation of processes involving diffusion, one of which is the irradiation damage.
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•We constructed new interatomic potential for W.•New potential is faster by two orders of magnitude than the GAP one.•Predicted self-diffusion coefficient in W agrees with the experimental data.•The diffusion coefficient deviates from Arrhenius equation at high temperatures.
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