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Understanding irradiation damage involves a multi-scale and multi-physics approach, integrating data from experiments, simulations and phenomenological models. This paper focuses on its early stages, specifically neutron-induced collision cascades in zirconium, as nuclear-grade zirconium alloys are widely used in fuel assemblies. We have gathered and analysed a significant sample of results from high-fidelity, large-scale molecular dynamics (MD) simulations, employing existing interatomic potentials and the two-temperature model to account for electron–phonon coupling. Our data can be directly applied to higher-scale methods. Furthermore, we carried out a comprehensive statistical analysis of the features associated with the defect production, including the number of defects, their distribution and size of the affected area. As a result, we developed a generative model of collision cascades that is parametric, hierarchical and stochastic, i.e. it takes into account a statistical nature of the phenomenon, is interpretable and shareable. This model has been developed with three primary objectives: to provide a sufficient descriptor of a cascade, to interpolate data obtained from high-fidelity simulations, and to demonstrate that the statistical model can produce representative distributions of primary irradiation defects. The results can be used to generate synthetic inputs for models at longer length and time scales, to provide fast approximations that take into account the morphology of introduced defects, and in general to serve as a powerful analytical tool. [ABSTRACT FROM AUTHOR]

[Display omitted] • Native point defects in Al 0.5 Ga 0.5 N are studied by first-principles calculations. • The preferable charge state, donor and acceptor properties of Al 0.5 Ga 0.5 N with different native point defects are obtained. • The thermodynamic transition energy level of Al 0.5 Ga 0.5 N with native point defect under varied charge states are summarized. • The photoelectric properties of Al 0.5 Ga 0.5 N with different native point defects are clearly revealed. To explore the formation mechanism of native point defects in high Al content AlGaN film, the first principles methods are applied to study the native point defects in Al 0.5 Ga 0.5 N. The different kinds of vacancies, interstitials, and antisites are investigated. The formation energies of Al 0.5 Ga 0.5 N with native point defects under different charge states and growth conditions are analyzed and compared. Then, the preferable charge state, donor and acceptor properties of Al 0.5 Ga 0.5 N with different native point defects are explicitly obtained. The results show that Al N , Ga N , Al i , and V N exhibit donor properties in p-type condition while V Ga , V Al , V N , and N Ga exhibit acceptor properties and can play roles as compensating center in n-type Al 0.5 Ga 0.5 N under metal rich condition. For N rich condition, V Ga , V Al , N Ga , and N Al are favorable acceptors in n-type Al 0.5 Ga 0.5 N. Meanwhile, the charge distribution and bonding state of Al 0.5 Ga 0.5 N with native point defects are explored. It is found the N atoms in N i and N Ga form covalent bond and ionic bond with atoms in Al 0.5 Ga 0.5 N. Moreover, the band calculation reveals that the removal of N atom in Al 0.5 Ga 0.5 N makes the conduction band fatter and the effective masses of electrons increase while the introduction of N point defects make the valence band flatter, increasing the effective masses of holes. Furthermore, the corresponding thermodynamic transition energy levels of defects under different charge states are summarized. It is found that the thermodynamic transitions for V N , N i , and N Al may likely to happen under certain conditions. The above studies yield a detailed and quantitative description of native point defects in Al 0.5 Ga 0.5 N, which helps to get a deeper insight to the growth and doping of AlGaN. [ABSTRACT FROM AUTHOR]

[Display omitted] • Various point defects in the Zn 2 (V,Nb,Ta)N 3 monolayers are investigated. • A favorable formation is found for the SV N -, SV Zn -, DV ZnN (out-of-plane) defects. • Defects can significantly alter electronic properties of Zn 2 (V,Nb,Ta)N 3 monolayers. • Defect-induced formation of trap states in the fundamental gap of Zn 2 (V,Nb,Ta)N 3 monolayers is observed. • A comprehensive STM analysis of all studied defects is conducted. Structural defects, including mono- and double- vacancies, commonly presented at the surface of two-dimensional materials (2D), including 2D ternary nitrides. These point defects can alter electronic structure of 2D ternary nitrides. In this work, density functional theory based simulations are utilized for a comprehensive characterization of point defects in Zn 2 (V,Nb,Ta)N 3 monolayers. The monovacancies of Z and N in Zn 2 (V,Nb,Ta)N 3 monolayers are found to have the lowest formation energy among all studied defects. The presence of the monovacancy of N leads to a blue shift of valance and conduction bands of the Zn 2 (V,Nb,Ta)N 3 monolayers and the formation of deep trap states in their fundamental gap in the vicinity of the Fermi level, while the presence of the monovacancy of Zn induces the formation of shallow trap states within the fundamental gap on the Zn 2 (V,Nb,Ta)N 3 monolayers. The scanning tunneling microscopy simulated images of point defects in Zn 2 (V,Nb,Ta)N 3 monolayers obtained in this work can facilitate the detection of these defects in experiments. Therefore, the theoretical characterization of defects in Zn 2 (V,Nb,Ta)N 3 monolayers presented in this work can provide helpful guidance for future experiments. [ABSTRACT FROM AUTHOR]

The paper considers electronic structure of pristine and defective nickel ferrite (spinel Ni Fe 2 O 4 ). The orbital ordering, band gap and charge transfer are studied in the framework of density functional theory with account of strong electronic correlations (DFT+U method). The possibility of changing the type of polaron transport in the presence of oxygen vacancies and nickel antisites has been demonstrated. The corresponding non-adiabatic activation barriers of polaron transport is considered. The resulting hopping energies are in general agreement with experimentally observed activation energies. The highlighted influence of point defects on the polaron conductivity mechanism could be a suitable explanation for the large variability of activation energies in previous experimental works. NEGF-DFT calculations were also performed to consider a possible band conduction mechanism. The enhanced conduction with the presence of oxygen bi-vacancies, and a change in carrier type is also observed. [Display omitted] • Two conduction mechanisms in NiFe 2 O 4 have been investigated in the DFT+U framework. • We show that point defects can change the carrier type of polaron hopping. • NEGF-DFT calculations suggest that oxygen vacancy filaments offer conduction channels. [ABSTRACT FROM AUTHOR]

[Display omitted] • A technique for identifying the grain boundary regions in irradiated nano-crystalline configurations has been developed. • The production efficiency of interstitials is significantly lower in nano-crystalline HEA FeCoCrNi/Ni than in their single- crystalline counterparts. • Most defect clusters in irradiated nano-crystalline materials comprise 1/2 〈1 1 0〉 stair-rod dislocation lines. • The nano-crystalline-HEA FeCoCrNi effectively prevents the formation of harmful large defect clusters. Because of remarkable irradiation resistance and mechanical properties, high entropy alloys (HEAs) are expected to be a candidate structural material in the next-generation nuclear power plants. Besides, the nano-crystalline (NC) materials also exhibit excellent radiation tolerance and good thermal stability. The NC-HEAs may have superior irradiation resistance than both NC and HEA materials. However, how the irradiation-resistant effects of HEAs and grain boundary (GB) jointly affect the irradiation damage evolution in NC HEAs is an interesting but rarely reported topic. Considering these, the present work investigated the irradiation defect production and accumulation characteristics in NC-HEA FeCoCrNi and NC-Ni by cascade overlapping simulations. The evolution of irradiation clusters within NC grains was quantitatively analyzed for the first time using a newly developed method. The results show that the irradiation defects produced in NC-HEA are more diminutive and uniformly distributed than those in NC-Ni with a similar irradiation dose despite the total number of survived point defects being very close in the two cases. Further investigation shows that such a better irradiation resistance of NC-HEA can be attributed to the synergy between the severe lattice distortion effect in HEAs and the interstitial sink effect of GBs in NC. The present study may provide some fundamental understanding of the irradiation defect evolution mechanisms for the novel HEAs that potentially serve as structural materials in advanced reactors. [ABSTRACT FROM AUTHOR]

An atomistic model of Cu-Ag core–shell nanowire using molecular dynamics is proposed. The simulation model was utilized for the evolution of temperature dependent (in the range of 10–500 K) tensile behavior and the identification of ductile-to-brittle transition temperature (DBTT) of single-crystal Cu-Ag core–shell nanowire. The evolution of defects such as point defects, dislocations, and stacking faults, arising from tensile deformation in the mentioned temperature rage were analyzed. The Wigner-Seitz Defect analysis, Dislocation analysis, and Common Neighbor analysis methods were implemented in this study to estimate the various defects concentration in the nanowire. The study identified that Cu-Ag core–shell (core diameter = 4 nm and shell thickness = 1 nm nanowire) exhibits DBTT somewhere in the temperature between 25 K to 30 K. The modulus of elasticity found to be increasing from 19.7 TPa at 10 K to 23.7 TPa at 30 K (within brittle regime), followed by a steep fall to 14.9 TPa at 500 K where fracture seems to be in ductile mode. The observed mechanical properties of the nanowire are discussed in the article in view of the dislocation and stacking faults generation in the core–shell nanostructures. [ABSTRACT FROM AUTHOR]

[Display omitted] Modulation doping in semiconductors has attracted much interest because of its ability to provide a reasonable concentration of free carriers without compromising their mobility, which is significantly reduced by conventional doping. It is very rare to find structures such as Bi 2 O 2 Se, which can be thought of as having a separate "doping part" (Se) and "conducting part" (Bi 2 O 2). Such a structure allows a high carrier mobility at reasonable carrier concentrations. These structures can be viewed as natural electronic composites and this process is often referred to as modulation or delta doping. In this study, we explore and discuss the possibilities of similar but artificial electronic composites − materials doped due to the presence of a foreign phase. Although, such a doping is probably almost ubiquitous in heterogeneous systems, it is very unlikely to provide a reasonably high and homogeneous concentration (1018 cm−3) of free charge carriers. Rather, the foreign phase often merely modifies the stoichiometry of the matrix and thus the concentration of native point defects and hence free charge carriers. However, our study shows that although the chance of achieving effective modulation doping is small for 3D structures, it increases significantly for both 1D and 2D structures for low-volume nanoinclusions (<10 nm3). This work also provides guidance on the proper choice of material pairs with respect to modulation doping. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • 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. [ABSTRACT FROM AUTHOR]

[Display omitted] • Helical dislocations generate significant normal stress in the direction parallel to their axis within the helix region. • The helix pitch has a greater impact on the intensity of stress within the helicoid dislocation than the helix diameter. • The helix's unfolding is controlled by the self-Peach-Koehler force, which is attributed to the shear stress components. Mutual interaction among microstructural elements, such as dislocations or point defects, through elastic fields plays an important role in understanding the dynamic evolution of microstructures in materials. For example, the ability of a helical dislocation to absorb extra point defects relies on the distribution of vacancy or interstitial around the helical dislocation line, which is determined by the elastic stress tensor. Therefore, to understand the kinetics and thermodynamics of crystallographic defects far from their statistical equilibrium, e.g., under irradiation, one needs to get an insight into the elastic stress field associated with helical dislocations. Using anisotropic linear elasticity theory, we investigate the elastic stress field induced by the helical dislocation line. Helical dislocations generate significant normal stress in the direction parallel to their axis within the helix region, while the other stress components are negligibly small. Furthermore, we elucidate the effect of geometrical parameters of helical structure, such as pitch length, diameter, and chirality, on the magnitude and distribution of the stress field. Atomistic simulation is also conducted to verify the elastic field modeling results further. [ABSTRACT FROM AUTHOR]

[Display omitted] • The lattice parameters of ZnO are modified through introduction Mn2+. • Mn2+ doped ZnO promotes the formation of V O • and inhibits the growth of Zn i. • Mn2+ doped ZnO enhances electrical conductivity by narrowing the band gap. • Regulation of intrinsic point defects can improve the electrical characteristic. Transition metal doping is considered one of the most effective approaches for enhancing the electrical properties of ZnO. The performance of ZnO is primarily influenced by intrinsic point defects present in the depletion layer. In this study, we employ first principles calculations to investigate the variation of intrinsic point defects impact of ZnO and Mn2+ substitution doped ZnO. Our findings reveal that Mn2+ substitution significantly improves the conductivity of ZnO by narrowing the band gap. Mn2+ substitution lattice Zn inhibits zinc interstitial formation and promotes oxygen vacancy growth via increasing zinc interstitial formation energy and decreasing oxygen vacancy formation energy. Simultaneously, Mn2+ can cause changes in ZnO crystal lattice. [ABSTRACT FROM AUTHOR]

[Display omitted] • Energy barrier values set for vacancy-assisted solute migration in Al alloys is given. • Results explain why the main age-hardenable alloy families are Al-Cu-Mg & Al-Zn-Mg. • Synergy between Mg & Ag explain why Ag enhance alloys' mechanical response greatly. • The energy values can be used to aid kMC simulations for large-scale alloy models. In this work, a consistent and accurate set of energy barrier values for the migration process, assisted by a vacancy, of atoms of different chemical elements belonging to the two most relevant families of age-hardenable Al-Cu and Al-Zn-based alloys is given. These values were calculated using the Nudged Elastic Band method within the Density Functional Theory framework for a vacancy diffusing in simple configurations of solute atoms, specifically the main alloying elements Cu and Zn involving a single solute atom or more complex configurations, such as pairs of elements of the same or different chemical species. In both cases, in our calculations, the presence of Mg and/or Ag solute atoms is also considered. The results obtained are analyzed in terms of the energetic interaction among vacancies and the different solute atoms. The advantage of having a set of vacancy diffusion energy barrier values calculated under the same criteria is that it can be used as reliable input parameters for future kinetic Monte Carlo simulations to study the precipitation kinetics in a wide type of age-hardenable alloys. [ABSTRACT FROM AUTHOR]

[Display omitted] High entropy alloys (HEAs) consist of multiple elements present in large proportions that are randomly distributed on a crystal lattice. On the one hand, the presence of multiple elements engenders wide ranges of atomic radii, electronegativities, electron valences and magnetic moments, whereas on the other, the presence of chemical randomness creates unique nearest neighbor environments among the lattice sites. As a result, the symmetry of the energy landscape is broken essentially at each lattice site thereby resulting in highly distorted energy landscapes. At the atomistic level, the lattice distortion has been widely observed in the form of varying bond lengths. At the electronic level, a range of charge transfers result in the charge density distortion. Collectively, the distorted landscapes cause large quantitative variations of the atomic level properties; in this review, we highlight the effect of lattice distortion on point defect energetics, stacking fault energies, and dislocation mobility. Besides the well-known large HEAs phase space, the enormity of the distorted energy landscape that scales with the atomic configurations is a new consideration; understanding this coupling between composition, lattice distortion and properties' variations thus becomes an exciting but challenging area within the field of HEAs. This coupling is expected to open a new door for materials design, where the materials properties could be tuned via leveraging the lattice distortion, which is essentially absent in dilute/ordered alloys. [ABSTRACT FROM AUTHOR]

[Display omitted] Under extended radiation exposure and elevated temperatures, helium (He) accumulation can compromise the integrity of Tantalum (Ta), a material showing substantial promise for nuclear fusion reactor applications. An imperative step towards understanding and enhancing the performance of Ta-based materials lies in the development of an accurate potential for Ta-He interactions. In this study, we introduce a neural network modified lattice inversion potential (NN-LIP) specifically designed for nuanced, element-specific Ta-He interactions. The conventional atomic density descriptors have been augmented to encompass sub-atomic characteristics, ensuring an accurate representation of varied local chemical environments across the energy spectrum. The lattice inversion potential for individual atoms introduces an atomic cross-potential, bolstering the transferability and robustness of NN-LIP, thereby amplifying its extrapolation capacity. Empirical calculations centered on pivotal properties of the Ta-He system affirm the precision of the multi-element NN-LIP potential. Our comprehensive dataset, spanning 19162 samples, covers a gamut from Ta bulk properties to point defects, He vacancies, and migration traits, achieving a validation set accuracy of 5.14 meV/atom. Notably, the migration barrier prediction accuracy displayed marked improvement over prior studies. The formulated multi-element NN-LIP offers a detailed examination of Ta-He interactions and holds potential for modeling analogous metal-helium interactions in nuclear substrates. [ABSTRACT FROM AUTHOR]

[Display omitted] Due to the highest conversion efficiency of β-CsPbI 3 among all the inorganic halide perovskite solar cells, it has attracted widespread attention. This paper systematically studies the formation energy and transition energy level of intrinsic point defects for β-CsPbI 3 by using first-principles. The results demonstrate that growth of β-CsPbI 3 is greatly affected by the Cs concentration and its growth window is extremely small. Although β-CsPbI 3 has some deep-level defects, the formation energies of these defects are relatively high with positive values. Both under Pb-rich and Pb-poor conditions, the transitional energy levels of main intrinsic acceptor defect Pb vacancy (denoted as V Pb) is in the valence band, which induces a high hole carrier concentration. Therefore β-CsPbI 3 is considered as an excellent p-type semiconductor. It might be used to as a potential candidate of inorganic perovskite materials for solar cell absorber. [ABSTRACT FROM AUTHOR]

The accuracy of interatomic interaction potentials – also known as force fields – is the main factor determining the physical soundness of classical molecular dynamics (MD) simulations. Here, we present a multi-objective framework to generate embedded-atom-method (EAM) force fields using ab initio data. The EAM force fields were tuned via particle swarm optimization to capture the non-linear association between atomic structures and system energies. Using this framework, 95 standard EAM force fields for zirconium were developed and 45 physical features for each developed force field were tracked. Principal component analysis (PCA) was performed to provide insights into the compromises that must be made when generating EAM force fields. Of note, by assigning large fitting weights to generalized stacking fault energy (GSFE) surfaces, there exist EAM force fields with properly positioned minima on prismatic GSFE surfaces and containing no spurious minima in basal GSFE surfaces. However, while standard EAM force fields achieved this without explicitly taking the angular dependence of atomic interactions into account, they led to a severe mismatch between other important physical properties and benchmarks. Hence, we also constructed two machine-learned tabulated Gaussian approximation potentials (tabGAP) with an additional three-body term, which successfully tackled the aforementioned issue and exhibit acceptable prediction accuracy across many physical properties (lattice parameters, elastic properties, dimer potential energies, melting temperatures, phase stability, point defect formation energies, point defect migration energies, and free surface energies) of Zr. Remarkably, its computational efficiency is only 6 times slower than standard EAM force fields. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, primary radiation damage in PuO 2 and (U 0.5 Pu 0.5)O 2 is investigated as a function of temperature (300–1500 K) using MD simulations with 5 keV cascade. UO 2 data from our previous work are used as reference. The interatomic potential develop by Cooper et al. has been used in this study. Time evolution of cascade generated defects is similar for different directions of primary knock on atom (PKA). Our results shows that the number of defects remaining after the cascade events in PuO 2 is higher than that in UO 2 at all temperatures. Defect concentration in (U,Pu)O 2 is observed to be in between that of the pure oxides. The number of residual defects decreases as the temperature increases and finally tends to approach a plateau at elevated temperatures. The concentration of residual anion defects is considerably higher than that of cations in all oxides, while a decrease in the ratio of anion to cation defects with increasing temperature is observed. At lower temperature, the annihilation efficiency (ξ) of defect follows the trend ξ PuO2 < ξ UPuO2 < ξ UO2. It is reported that both pure and mixed oxide fuels form defect clusters in the residual damage. The fraction of interstitial clusters is higher than the vacancy clusters; however, the size of these clusters is smaller than that of voids. [ABSTRACT FROM AUTHOR]

• Molecular dynamics simulations were used to investigate the effect of the presence of carbon atoms in low-carbon α-Fe containing a symmetric tilt grain boundary (STGB) on the number of interstitials and vacancies produced by displacement cascades. • The cohesive energy of Fe atoms and C atoms in the α-Fe matrix was estimated to be E Fe = - 4.01292 C + - 2.9728 e - 6 and E C = - 15.34462 C + - 9.16691 e - 5. • GB energies of the structures for 17 110 STGBs as a function of the GB angle for 27 different at.%C ranging from 0.0058% to 0.1569% was calculated and a deep cusp at GB misorientation of θ = 90 ° was observed. • The results of the thermal spike stage and the consequent recombination stage showed that the PKA energy and the presence of GB in Fe-C have no effect on the time at which point defects reach to their maximum values at the thermal spike stage. • The results showed that the number of defects in the presence of GB drops in comparison to the number of defects produced in the case of Fe-C without GB planes. • The results showed that carbon, either dispersed form or C-rich region in α-Fe, has no meaningful effect on the number of residual point defects. In this paper, molecular dynamics simulations were used to investigate the effect of the presence of carbon atoms, either in dispersed form or C-rich region, in low-carbon α-Fe containing symmetric tilt grain boundary (STGB) with a boundary plane rotated about the 110 misorientation axis on the number of SIAs and vacancies produced by PKA energies of 3, 5, 7 and 9 keV at 300 K. Results were compared with the SIAs and vacancies produced in pure α-Fe. It was also shown that the presence of GBs in this Fe-C alloy has no effect on the time at which point defects reach to their maximum values at the thermal spike stage. On the other hand, the GBs decrease the number of point defects in comparison to Fe-C without GB planes. It was also concluded that the carbon, either in dispersed form or C-rich region, has no meaningful effect on the number of survived point defects. Furthermore, the number of SIAs is less than the number of vacancies, except at θ = 90 °. This result was attributed to GB energy because by calculating GB energies as a function of the GB angles for 27 different at.%C ranging from 0.0058% to 0.1569%, a deep cusp was obtained at θ = 90 °. A sharp rise and fall were observed for the number of SIAs and vacancies at θ = 90 ° misorientation, respectively. The sharp rising becomes smooth for the number of SIAs with increasing E PKA and the sharp falling becomes deeper for the number of vacancies with increasing E PKA. [ABSTRACT FROM AUTHOR]

• Point defect transformations can accelerate potential energy surface explorations. • Implemented according to three regimes: interstitial, neutral, and vacancy rich. • Application on fullerene clusters demonstrates new explorations pathways. • Energy super-basin history list enables further enhanced sampling during operation. The free and potential energy surfaces (F/PES) of atomistic systems contain important information regarding structural stability that is crucial in the development of new materials and devices. An effective method for navigating the energy surface can help to realize new synthesis pathways, fabrication techniques, and aid in the prediction of complex atomic structures. In most physical systems, an accurate exploration of the most stable atomic configurations in the FES can be computationally prohibitive using traditional, temperature dependent Monte-Carlo and dynamics based techniques due to the large spatial rearrangements and long time scales involved. In this work, we demonstrate the role of point defect (PD) mediated processes in navigating the PES by implementing PD transformations in a conventional PES exploration technique in order to enable shortcuts in finding the global energy minimum. Using the standard minima-hopping method as a means of sampling the PES, we discuss the details of a point defect mediated Minima-Hopping (PDMH) approach. We study the necessity of incorporating classification and biasing techniques during the search, such as a funnel characterization procedure with an accompanying super-basin history list. An example of our method is demonstrated on fullerene clusters starting from known, nearby low energy configurations. The results show that our method can enable pathways toward the global minimum energy configuration where an optimized MH calculation could not. The implications of such a method are discussed along with future areas of development. [ABSTRACT FROM AUTHOR]

• New interatomic potentials of Ta-Ta and W-Ta based on F-S formalism have been developed. • The formation energies of point defects and the non-degenerate core structure of a 1/2 〈1 1 1〉 screw dislocation in Ta bulk are well reproduced. • The developed potentials have high accuracy and good transferbility. • These potentials are applicable for describing the evolution of point defects in Ta and W-Ta alloys. Tungsten (W) and W-based alloys are regarded as the most promising candidates for plasma facing materials (PFMs) in future fusion reactors. In this work, new interatomic potentials for Ta element and W-Ta alloy have been developed based on the Finnis-Sinclair formalism, in combination with our previously developed potential for W. The potential parameters for Ta were determined by fitting to a set of experimental and first-principles data, including lattice constant, cohesive energy, elastic constants, point defects formation energies and Rose's equation of state for the bcc lattice. The W-Ta cross parameters were fitted to the first-principles data of the formation energies and binding energies of Ta atom with different point defects in bulk W. The present potentials not only reproduce some important physical properties of various point defects, but also predict the non-degenerate/compact core structure of the 1/2 〈1 1 1〉 screw dislocation in bulk Ta, which is the same as DFT calculations. The developed potentials were expected to be suitable for atomistic simulations of point defects evolution in Ta and W-Ta binary alloys. [ABSTRACT FROM AUTHOR]

Zinc sulfide (ZnS) based materials are widely used in many applications. Yet, due to a lack of detailed knowledge of defect energy levels, the electrical properties and luminescence mechanisms in the materials still give rise to debate. Here, we report a first-principles study of native point defects and impurities in zincblende ZnS using hybrid density-functional calculations. We find that cation and anion vacancies and antisite defects introduce deep defect levels in the band gap and can act as donors or acceptors depending on the position of the Fermi level. The substitutional impurity Cu Zn acts as a deep acceptor and thus does not contribute to p-type conductivity. Substitutional impurities Al Zn and Cl S , on the other hand, are shallow donors. More importantly, we identify the isolated (i.e., unassociated) Cu Zn as a source of the green luminescence observed in ZnS-based phosphors and Cu Zn – Al Zn and Cu Zn – Cl S defect complexes as sources of blue luminescence. The materials may have both green and blue emissions with the relative intensity dependent on the ratio between the unassociated defect and defect complex concentrations, which is also consistent with experimental observations. [ABSTRACT FROM AUTHOR]

The two-temperature model has been applied to investigate the effects of the electronic subsystem on 150 keV Ni ion cascades in nickel using molecular dynamics simulation. We explore the effects of the magnitude of the electron-phonon coupling and the electronic thermal conductivity on defect production and cluster formation. It has been found that stronger electron-phonon coupling allows larger and more rapid energy feedback to the atomic subsystem, leading to reduction of number of point defects and suppression of the formation of larger defect clusters. It was observed that larger electronic thermal conductivity results in slightly increased number of point defects and larger size vacancy clusters. The latter takes place because of suppression of point defects recombination in faster cooling areas of initial damage. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Charged impurities influence functional properties of two-dimensional materials and a detailed theoretical understanding of charged defects is required to enable a rational design of defect-engineered nanomaterials for applications in ultrathin devices. To achieve this goal, we have developed multiscale approaches that combine atomistic first-principles theories, such as density-functional theory, with coarse-grained continuum models, such as effective mass models. This allows us to model large supercells which are required to accurately describe the slow decay of the screened defect potential and the defect-induced changes in the electronic properties of the two-dimensional host material. I will describe the results of our multiscale calculations for charged defects in doped graphene and in transition-metal dichalcogenide monolayers which have revealed novel mechanisms for controlling and tuning the electronic structure of two-dimensional materials. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Carbon vacancies are easily produced in Ti 2 CO 2. • The electronic properties of Ti 2 CO 2 with different defect concentrations are investigated. • Carbon vacancy configuration distribution has little influence on the electronic conductivity. • The oxygen vacancy induced band gets localized with the nearly flat band dispersion. • Oxygen vacancy configuration distribution changes the electronic band structures at the Fermi level. Abstract The stabilities and electronic properties of vacancy-doped Ti 2 CO 2 have been investigated by a first-principles method. The formation energies of carbon (C) vacancies are relatively small. And they change from negative to positive as the defect concentration of C vacancies increases. Atomic-vacancy-induced defect states appear in the band structure of defective Ti 2 CO 2. The Fermi energy of C vacancy (V C)-doped Ti 2 CO 2 shifts upward compared with that of perfect Ti 2 CO 2 , making V C -doped Ti 2 CO 2 exhibit metallic character. A localized defect state of oxygen vacancy (V O)-doped Ti 2 CO 2 occurs in the midgap of pristine Ti 2 CO 2. And as the defect concentration decreases, the V O -induced band becomes more localized with nearly flat band dispersion. The defective state of V O -doped Ti 2 CO 2 acts as an electron donor state when Ti 2 CO 2 is used as a semiconducting material. Further, the stabilities and electronic properties of different C and O divacancy configurations are explored. Investigation of the C divacancy (V 2C) in a 4 × 4 × 1 Ti 2 CO 2 supercell indicates that the C vacancy configuration distribution has little influence on the electronic conductivity of V 2C -doped Ti 2 CO 2. Hence it is possible to modulate the electrical conductivity of Ti 2 CO 2 by adjusting the C vacancy concentration. Investigation of the O divacancy (V 2O) suggests that the O vacancy configuration distribution changes the electronic band structure at the Fermi level of V 2O -doped Ti 2 CO 2. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Since their discovery in 2011, interest in MXenes, two-dimensional transition metal carbides and/or nitrides, has greatly expanded due to their promising functional properties and facile synthesis methods, and their development for emerging technologies is propitiously progressing. Despite promising advancements, there still remains a lack of understanding with regards to their fundamental mechanical properties. Here, nanoindentation of the Ti n+1 C n T x MXenes was studied via atomistic simulations utilizing a parametrization of the ReaxFF interatomic potential, to understand the influence of point defects. From force-displacement curves, the Young's moduli of pristine Ti 3 C 2 O 2 and Ti 2 CO 2 were calculated to be 466 GPa and 983 GPa, respectively. The influence of both titanium and carbon vacancies (V Ti and V C) on Ti 3 C 2 O 2 were also quantified using simulated nanoindentation of a set of samples containing both 1% V Ti and 10% V C , resulting in a reduction of the calculated Young's modulus to 386 ± 31 GPa. Of particular importance, is that these results mirror recent experimental findings indicating the fundamental role of defects in the mechanical behavior of MXenes. The calculated modulus in this work for the defect-containing Ti 3 C 2 O 2 surpasses that of graphene oxide, establishing it as a new benchmark in strength for solution-processed, 2D materials. Results here also indicate improvements can be made in current MXene processing methods to better approach the theoretical strength of pristine 2D materials. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract The potential use of GaN/ZnO heterojunction as a magnetic material has been neglected because its magnetic properties are rarely studied. In this study, the magnetic properties of GaN/ZnO heterojunction interface are systematically calculated, and the effect of electric polarization intensity on the spin-electron was analyzed. Results showed that GaN/ZnO heterojunction interface exhibits a semiconducting feature. The magnetism of GaN/ZnO heterojunction interface is mainly affected by two factors. The first factor is the number of unpaired p-state electrons induced by cation vacancies, and the magnetism in the heterojunction interface originated from the spin polarization of these p-state electrons. The second factor is the electric polarization intensity in the heterojunction interface. If the electric polarization intensity is too low, then the unpaired p-electrons cannot be spin-polarized to produce a net magnetic moment. The spin polarization of p-state electrons increases with the increase in electric polarization intensity. Excessive electric polarization intensity inverts the spin direction of a part of p-state electrons, and ferromagnetic–ferrimagnetic–antiferromagnetic transition occurs in the heterojunction interface. Therefore, the magnetic property of GaN/ZnO heterojunction interface can be controlled by varying the electric polarization intensity. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • New consistent consistent set of interatomic potentials for monazites and xenotimes. • Errors do not exceed 0.3% in the calculation of structural parameters. • Calculated formation energies of point defects and enthalpy of mixing. • Results are consistent with experimental data. Abstract We have calculated the structural and thermodynamic parameters for solid solutions of lanthanides and plutonium monazites and xenotimes using the developed consistent set of interatomic potentials. We have estimated energies of the point defects of crystal structures. The developed model can be applied for further modelling of radiation stability of Pu-containing monazite using molecular dynamics approach. [ABSTRACT FROM AUTHOR]

[Display omitted] The effect of a 1/2[1 1 1] screw dislocation on the growth of helium bubble in tungsten is investigated by molecular dynamics simulation method. When helium bubble grows at sites less than 3 nm away from the dislocation, tungsten self-interstitial atoms (SIAs) pushed out by the growing bubble are absorbed by and then migrate rapidly along the dislocation line, inducing the screw dislocation to evolve into a helical configuration. The existence of screw dislocation can facilitate the growth of helium bubble. The interaction energies between the screw dislocation and point defects (helium, SIA and vacancy) are calculated. The interaction energies are all negative, indicating that the screw dislocation can attract and serve as a sink for these point defects. Further investigation shows that the interactions between the screw dislocation and these point defects are local, and stem from the special stress distribution pattern of the screw dislocation. [ABSTRACT FROM AUTHOR]

The structural, electronic and magnetic properties of single-layer α-Ga 2 S 3 with intrinsic point defects, including five vacancy defects, three interstitial defects, and five antisite defects, are systematically investigated. [Display omitted] • The point defects properties of single-layer semiconductor α-Ga 2 S 3 are complicated, since there are nonequivalent Ga and S atomic sites. • The stability, midgap states and magnetism of five vacancy defects, three interstitial defects, and five antisite defects are investigated. • The origin of the midgap states and magnetic moments of the defects are also investigated. Motivated by recent experimental realization of single-layer α-Ga 2 S 3 [Zheng et al. , Adv. Funct. Mater. 31, 2008307(2021)], by using first principles calculations, we systematically investigated the structural, electronic and magnetic properties of single-layer α-Ga 2 S 3 with intrinsic point defects. Although it is a binary semiconductor, its point defects properties are complicated, since there are nonequivalent Ga and S atomic sites in this compound. The most energetically stable vacancy and interstitial defect are V S2 and S i1 for the entire sulfur chemical potential range, while the most energetically favorable antisite defect is dependent on the sulfur chemical potential, such as Ga S2 under S-poor condition and S Ga1 (S Ga2) under S-rich condition. The sulfur vacancy defects (V S1 , V S2 and V S2) have induced spin-degenerated defect states in the band gap or the valence band edge, while the gallium vacancy defects (V Ga1, and V Ga2) have spin-polarized defect states in the band gap or valence band edge with the magnetic moment of 1.30 μ B and 1.21μ B per defect. The interstitial defects (Ga i1 , S i1 and S i2) can generate spin-degenerated in-gap defect states. The antisite defects (Ga S1 , Ga S2 , Ga S3 , S Ga1 , and S Ga2) have spin-polarized in-gap defect states with weak magnetic moments of 0.70 μ B , 0.69μ B, 0.64μ B, 0.66μ B and 0.65μ B per defect. Besides, the origin of the defect states and magnetic moments are examined in detail. These findings are helpful for understanding the defect properties of two dimensional III A- VI A binary chalcogenide Ga 2 S 3 and improving its technological applications. [ABSTRACT FROM AUTHOR]

CeO 2 (ceria) is a material of significant industrial and technological importance, used in solid oxide fuel cells and catalysis. Here, we explore the usage of linear-scaling density functional theory as implemented in the ONETEP code, which allows to use larger simulation cells. By using DFT+ U calculations we revise the defect chemistry of ceria, including point defects, Frenkel and Schottky defects. We found that the ground state of an oxygen vacancy is associated to two neighbouring reduced cerium sites. A cerium vacancy is the least favourable point defect, where holes localise on neighbouring oxygen sites. It is more favourable to displace an oxygen interstitial defect away from the octahedral interstitial site, with the formation of a stable peroxide species. Our simulations show that a cerium interstitial is best accommodated in the octahedral interstitial site, as this minimises the distortion of the lattice. Placing a vacancy and an interstitial defect at a separation of 5.18 Å for the OF¡110¿ and 4.77 Å for the CeF¡111¿, stable Frenkel defects can be formed. We also studied the effect of different supercell size on the energetic ordering of Schottky defects, where the S¡111¿ is more favourable than the S¡110¿ for a given simulation cells containing 324 or more atoms. • Linear-scaling density functional theory simulations with bulk materials. • Large simulation cells containing defects in bulk cerium oxide. • Point defect formation at more dilute concentrations. • Structural and electronic properties of point defects. • Energetic ordering of Frenkel and Schottky defects at increasing simulation size. [ABSTRACT FROM AUTHOR]

Highlights • UO 2 produces more defects than ThO 2 in 5 keV cascade event between 300 and 1500 K. • Number of residual defect in (U 0.5 Th 0.5)O 2 is much higher than in UO 2 or ThO 2. • Residual defect concentration decreases with the increase in temperature. • Damaged structure contains clusters of defect in both pure and mixed oxide fuel. • Vacancy clusters are larger, however less frequent than interstitial counterparts. Abstract Primary radiation damage in UO 2 , ThO 2 and (U 0.5 Th 0.5)O 2 has been investigated as function of temperature (300 to 1500 K) using classical molecular dynamics (MD) simulations. Displacement cascades of 5 keV are used for defect production. The number of defects produced from the cascade events in UO 2 is higher than that in ThO 2 at all temperatures. Our results indicate that the defect production in (U 0.5 Th 0.5)O 2 is different from that in the pure oxides. The number of residual defects in the mixed oxide fuel is considerably higher than in UO 2 or ThO 2. In all three systems studied, the fraction of anion defects is much higher than that of cations, in line with higher defect energies of the U sublattice compared to the O sublattice. It is also reported that for increasing temperature peak damage increases, while residual damage decreases. This is indicative of the greater recombination of defects due to enhanced mobility at high temperatures. All systems studied exhibit clustering in the residual damage with interstitial clusters tending to be smaller than voids. [ABSTRACT FROM AUTHOR]

The point defect effects on phonon thermal conductivity of bulk crystalline β -SiC at 750 K and 1098 K are calculated with reverse non-equilibrium molecular dynamics method. Quantum correction is used to correct the corresponding temperatures. By extrapolation and quantum correction, the results of thermal conductivity of bulk β -SiC with point defects are achieved and corrected. For the eight types of point defects studied in this work, the thermal conductivity of SiC decreases with the increase of the concentration of certain point defects. The thermal conductivity drops rapidly at low concentration condition and gradually reaches certain value at high concentration condition. At high defect concentration condition, the temperature does not affect the thermal conductivity too much. The additional thermal resistivity is proportional to the concentration of all types of the point defects we studied. In these point defects, the interstitial Si TC decreases the thermal conductivity of β -SiC the most. On the other hand, the interstitial C TSi affects the thermal conductivity the least. [ABSTRACT FROM AUTHOR]

Vacancy defects in 2D materials provide opportunities to tailor local physical, structural and electronic properties of point and linear vacancies in Janus MoSSe monolayers. In this paper, we studied vacancy formation in Janus MoSSe monolayers using ab initio density functional theory and observed that all vacancies are preferentially formed in the Se layer. In the case of point defects with more than two vacancies, a zigzag line feature is obtained for the lowest formation energy. In the case of infinite linear defects, the zigzag vacancy lines preferred to be distant from each other. The bandgap of a Janus MoSSe monolayer can be modulated by the concentration of vacancies. The bandgap energy decreased from 1.080 eV to 0.675 eV with the increase in the number of point vacancies. However, it is observed to oscillate around 0.530 eV with the increase of distance between the vacancy lines in the case of linear vacancies. This work is very useful in bandgap engineering of optical and electronic devices based on MoS 2 . [ABSTRACT FROM AUTHOR]

In metallic alloys of fission or fusion reactors, microstructural evolution results from a dynamic equilibrium between thermodynamic forces and the production of defects by irradiation. The migration of defects can lead to the formation of clusters of defects (nano-cavities, dislocation loops, nano-precipitates) or variations in chemical composition close to the defect sinks, a phenomenon known as Radiation Induced Segregation (RIS). To predict the effect of irradiation conditions (type of irradiation particle, dose rate, temperature), phenomenological diffusion models exist that have to be assembled to give an overall description. Our objective is to describe these models and to propose numerical implementations to solve them starting at the atomic scale (DFT energy calculations, Kinetic Monte Carlo, Self-Consistent Mean Field approaches) to reach the mesoscopic one using the phase field modeling. This multi-scale approach is illustrated by a short review of recent studies focusing on dilute and concentrated iron based alloys. [ABSTRACT FROM AUTHOR]

The formation and lifetime of point defects is governed by an interplay of kinetics and thermodynamic stability. To evaluate the stability under process conditions, empirical potentials and ab initio calculations at T = 0 K are often not sufficient. Therefore, various concepts to determine the full temperature dependence of the free energy of point defects with ab initio accuracy are reviewed. Examples for the importance of accurately describing defect properties include the stabilization of vacancies by impurities and the non-Arrhenius behaviour of vacancy formation energies due to anharmonic lattice vibrations. [ABSTRACT FROM AUTHOR]

The projector augmented wave method was applied to investigate the energetics of point defect formation at finite temperatures and the Ni-vacancy jumps in the intermetallic B 2-TiNi alloy. It was shown that the effective formation energy of the Ni-vacancy (1.14 eV) is significantly lower than that of Ti-vacancy (1.74 eV); however, the antistructural atoms are dominant defects irrespective of alloy composition. The obtained results reveal that the migration barrier of the Ni-vacancy to the nearest-neighbor site is less (0.19 eV) than that for the Ni-vacancy jump to the next-nearest-neighbor site (1.64 eV). The Ni-vacancy implements two sequential nearest-neighbor jumps with short-lived intermediate configuration and some of such jumps initiate six-jump cycles of the Ni-vacancy along [0 0 1] and [1 1 0] directions with [0 0 1] bent mechanism as preferential one. In the latter case the calculated migration barrier of 0.82 eV is found to be in good agreement with experiment. The energy barrier for four-jump cycle flat mechanism is calculated by 0.27 eV higher. It is shown that the Ni-vacancy diffusion in B 2-TiNi is strongly dominated by both six-jump cycle [0 0 1] bent and flat mechanisms at low temperatures but the contribution of the next-nearest-neighbor jumps become important with temperature increase. [ABSTRACT FROM AUTHOR]

Different descriptions used to model a point-defect in an elastic continuum are reviewed. The emphasis is put on the elastic dipole approximation, which is shown to be equivalent to the infinitesimal Eshelby inclusion and to the infinitesimal dislocation loop. Knowing this elastic dipole, a second rank tensor fully characterizing the point-defect, one can directly obtain the long-range elastic field induced by the point-defect and its interaction with other elastic fields. The polarizability of the point-defect, resulting from the elastic dipole dependence with the applied strain, is also introduced. Parameterization of such an elastic model, either from experiments or from atomic simulations, is discussed. Different examples, like elastodiffusion and bias calculations, are finally considered to illustrate the usefulness of such an elastic model to describe the evolution of a point-defect in a external elastic field. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the mechanical properties of a new two-dimensional graphene like material, crystalline carbon nitride with the stoichiometry of C 3 N. The extraordinary properties of C 3 N make it an outstanding candidate for a wide variety of applications. In this work, the mechanical properties of C 3 N nanosheets have been studied not only in the defect-free form, but also with critical defects such as line cracks and notches using molecular dynamics simulations. Different crack lengths and notch diameters were considered to predict the mechanical response at different temperatures under the uniaxial tensile loading. Our simulation results show that larger cracks and notches reduce the strength of the nanosheets. Moreover, it was shown the temperature rise has a weakening effect on the tensile strength of C 3 N. Our study can provide useful information with respect to the thermo-mechanical properties of pristine and defective graphene like C 3 N 2D material. [ABSTRACT FROM AUTHOR]

We introduce a long-range interaction analytical embedded atom method (namely la-EAM) interatomic potential, which has been developed by fitting the lattice constants, cohesive energy, mono-vacancy formation energy and elastic constants of α -Zirconium. We validate this la-EAM potential by extensive investigation of the bulk, surface, and defect properties of Zirconium using molecular dynamics simulations compared with available experiments and theoretical results. We examine the lattice constants, cohesive energy, elastic constants, phonon dispersion curves of α -, β-, and ω- Zirconium and find a good agreement with available experiments. We have studied the 0D (zero-dimension) defects including vacancies and self-interstitial atoms, 1D defects (dislocations), 2D defects including surface and stacking fault, and 3D bulk properties. Furthermore, our phase transformation energy barrier of α  →  ω agrees with the experimental observation. The success of our potential could attribute to the correctly accounting for the long-range interactions of the Zr atoms. Our results suggest that the developed la-EAM potential of Zr is useful in molecular dynamics simulations of bulk, surface and defect properties and phase transitions of Zirconium at various temperatures and pressures. [ABSTRACT FROM AUTHOR]

The formation energies, diffusion barriers, vibration frequencies of complex iodine defects in 3C-SiC are calculated. The effective diffusion rates of these complex defects are evaluated in the temperature range from 300 K to 2000 K. The iodine interstitial diffusion is the dominant diffusion mechanism in bulk SiC since its diffusion energy barriers is the lowest. On the contrary, if the iodine atom substitutes a Si or a C atom, the diffusion rate is the lowest. The diffusion rates of other iodine point defects coupled with vacancies are between the rates of these two cases. The vacancies near the iodine atoms are traps for the iodine and they can slow down the diffusion rate of iodine atoms. The experimental diffusion rate of iodine in SiC is between that of calculated interstitial and substitutional iodine. It may result that the experimental data is from the combination of all the point defect diffusion mechanisms. [ABSTRACT FROM AUTHOR]

Remarkable properties of ultra-high strength, ductility, and stability have been achieved through the introduction of twin boundaries in nanostructured metals. Here, we report molecular dynamics simulations which elucidate the synergistic role of grain boundaries and twin boundaries in enhancing the radiation tolerance of nanotwinned metals. While grain boundaries are known to be excellent sinks for point defects, coherent twin boundaries do not absorb point defects. A beneficial corollary is that the structural integrity of coherent twin boundaries remains intact as radiation-induced defects pass through them and ultimately get absorbed into grain boundaries. Hence, the twin boundaries can continue to play a role in imparting high strength even after being subjected to irradiation. Thus, nanotwinned structures may indeed be optimal motifs for radiation tolerant materials that preserve high strength and ductility. [ABSTRACT FROM AUTHOR]

Point defects, particularly vacancies, exist abundantly in the structure of a variety of clay minerals (e.g., kaolinite). Such defects significantly alter the physical/chemical characteristics of the minerals. Dissolution of kaolinite in an alkali medium is a critical step in the geopolymerization process and it determines the properties of the final product. In this work, a series of molecular dynamics (MD) simulations were carried out in the isothermal-isobaric (NPT) ensemble at 298 K and 1 atm to study the influence of structural vacancies (Al and Si vacancies in particular) on the interaction/dissolution of the two basal surfaces of kaolinite (partially deprotonated octahedral and tetrahedral surfaces) exposed to alkali media. Two different alkali media were used. One contained sodium cation (Na + ) only while the other potassium cation (K + ) and their concentrations were 3 M and 5 M. The MD results showed that regardless of the type of cation and cation concentration, Al vacancies on the octahedral surface promoted the dissolution of Al into the solution compared to the surface without Al vacancies. However, there existed a vacancy concentration (2 Al vacancies per 576 Al atoms) at which the dissolution amount was the maximum and above which the dissolution decreased with increasing Al vacancy concentration. The presence of Si vacancies in the tetrahedral surface did not show significant effect on the dissociation of Si. Radial distribution function (RDF) analyses indicated that the degree of crystallinity of the octahedral surface decreased as the number of Al vacancies increased but this was not the case for the tetrahedral surface. [ABSTRACT FROM AUTHOR]

Based on first-principles plane wave method within density functional theory using the generalized gradient approximation, we investigate the effects of point defects on the electronic and magnetic properties of single-layer phases of AsP. We predict that these properties of buckled and asymmetric washboard structures of AsP can be modified by various kind of point defects including single and divacancy, antisite and substitutions. While single-layer buckled AsP structure displays semiconducting properties, it becomes either metal or narrow band gap semiconductor in the presence of point defects. On the other hand, the nonmagnetic direct-gap semiconductor asymmetric washboard AsP is found to be metallic upon defect creation. All the creation of point defects have zero net magnetic moment, except asymmetric washboard phase of AsP with P vacancy. We calculated μ = 1.19 μ B for relaxed structure of the P-single vacancy. Our results show that free-standing single-layer phases of AsP functionalized by point defects can serve as interconnects between AsP based spintronic devices. [ABSTRACT FROM AUTHOR]

The main innovative issue of this paper is the calculation of kinetic coefficients using ab initio DFT wave functions. In the framework of short-range scattering models the calculations of transition probabilities presented without fitting parameters for electron interaction with polar and nonpolar optical phonons, piezoelectric, acoustic phonons and ionized impurities. Transition matrix elements have been evaluated by the numerical eigenfunctions obtained within the ab initio density functional theory (DFT). It is used here in the generalized gradient approximation (GGA) suggested by Perdew, Burke and Ernzerhof. For the first time temperature dependences of calculated CdTe electron mobility and Hall factor in the range of 10–1210 K are well compared with experiment. For the first time seven scattering mechanisms are treated without fitting parameters. It is shown that short-range scattering models describe qualitatively and quantitatively the experiment in comparison with long-range scattering models. [ABSTRACT FROM AUTHOR]

We study the electron transport in metallic carbon nanotubes (CNTs) with realistic defects of different types. We focus on large CNTs with many defects in the mesoscopic range. In a recent paper we demonstrated that the electronic transport in those defective CNTs is in the regime of strong localization. We verify by quantum transport simulations that the localization length of CNTs with defects of mixed types can be related to the localization lengths of CNTs with identical defects by taking the weighted harmonic average. Secondly, we show how to use this result to estimate the conductance of arbitrary defective CNTs, avoiding time consuming transport calculations. [ABSTRACT FROM AUTHOR]

The δ-MnO 2 has a layered structure and is expected to be a good absorbing material. Here, CASTEP was used for a theoretical study of the microwave absorption properties of δ-MnO 2 with defects (interstitial and substitutional cobalt atoms, vacancies). The results show that by analyzing the density of states (DOS) and partial density of states (PDOS), the defects change the charge distribution and increase the magnetic moment (increased by about 19 orders of magnitude). The bond length increased from 1.979 Å to 1.980 Å after substitutional defects formed to enhance the displacement polarizability. The changes in the charge distribution increase the atomic polarizability. The presence of crystal defects enhances both the magnetic loss and dielectric loss. In addition, the calculated defect formation energies show that the Co atoms tend to form interstitial atoms in MnO 2 (−16.90 eV), and the oxygen vacancy defects (−0.77 eV) are more easily formed than the manganese vacancy (33.14 eV). [ABSTRACT FROM AUTHOR]

The stability and clustering behavior of fission products (Zr, Mo, Ru, and Rh) in thorium dioxide have been investigated by density functional theory. The calculations were performed considering the possible insertion sites in ThO 2 , including interstitial sites, thorium vacancies, oxygen vacancies, the oxygen–thorium divacancy, and three types of Schottky defect. The thorium vacancy is the most energetically favorable trap site for all of these fission products. Zr and Mo can exist as oxide precipitates whereas Rh and Ru tend to form metallic clusters in ThO 2 . Moreover, Ru and Rh dimers are the most stable clusters in the Schottky defect in ThO 2 , suggesting that metal clusters in ThO 2 may be formed of these dimers trapped in Schottky defects. [ABSTRACT FROM AUTHOR]

While molecular dynamics simulations have been used for decades to study structure and formation mechanisms of plastic damage in crystals, the analytical tools needed to characterize collections of plastic defects have been limited. Here we demonstrate the use of two methods, spatial cross-correlations (CC) and Linear Discriminate Analysis (LDA), to analyze and compare plastic damage profiles among molecular dynamics simulations in which damage was created by straining bi-crystals containing symmetric tilt grain boundaries with different tilt angles. Two potentials were used, one representing Cu and one representing Ag, and two coarse-grained descriptors for different types of crystal damage were used, averaged central symmetry parameters (CSP) and atomic hydrostatic stress (HS). We find that in general the CSP is a more accurate descriptor than HS for both analysis methods, and for data base sizes of about 30 or more simulations per tilt angle, the LDA does considerably better in predicting angle and material than the CC method. For example, at the largest data base size of 50 simulations per tilt angle and using the average CSP values, the LDA predicts the exact initial tilt angle and material type for 92% of the simulations, while the CC approach drops to 58%. If the average HS is used instead of the average CSP, the LDA and CC predictions drop to 63% and 32%, respectively. These results point to a number of possible applications of this method, for example in quantifying how the range of damage for a set of strained systems may depend on strain rate or temperature, or quantifying similarities between complex damage from processes such as indentation and energetic ion bombardment. [ABSTRACT FROM AUTHOR]

A complete and rigorously validated open-source Python framework to automate point defect calculations using density functional theory has been developed. The framework provides an effective and efficient method for defect structure generation, and creation of simple yet customizable workflows to analyze defect calculations. The package provides the capability to compute widely-accepted correction schemes to overcome finite-size effects, including (1) potential alignment, (2) image-charge correction, and (3) band filling correction to shallow defects. Using Si, ZnO and In 2 O 3 as test examples, we demonstrate the package capabilities and validate the methodology. [ABSTRACT FROM AUTHOR]

Although GaN-based materials have been successfully utilized in optoelectronic and electronic devices, some important physical issues have not been fully understood, for example, why they can have high luminous efficiency even with high density of point defects, and what are the origins of yellow luminescence (YL) in their photoluminescence (PL) spectra. In this paper, the influence of point defects on GaN-based materials are investigated by first principle calculation. It is revealed that vacancy defects in GaN-based materials only make the effective masses of electrons and holes increase, consequently they have no significant contribution on the non-radiative recombination. What is more, C O complex interstitial impurities or Ga interstitial impurities are most likely to lead to YL in PL spectra of GaN-based materials. [ABSTRACT FROM AUTHOR]

We report a new attempt to study properties of Zr-Nb structural alloys. For this purpose we constructed an angular-dependent many-body interatomic potential. The potential functions were fitted towards the ab initio data computed for a large set of reference structures. The fitting procedure is described, and its accuracy is discussed. We show that the structure and properties of all Nb and Zr phases existing in the Zr-Nb binary system are reproduced with good accuracy. The interatomic potential is appropriate for study of the high-pressure hexagonal ω -phase of Zr. We also estimated characteristics of the point defects in α -Zr, β -Zr and Nb; results are proven to correlate with the existing experimental and theoretical data. In case of α -Zr the model reveals anisotropy of the vacancy diffusion, in agreement with previous calculations and experiments. The potential provides an opportunity for simulation of Zr-Nb alloys based on α -Zr and β -Zr. This conclusion is illustrated by the results obtained for the alloys with different niobium concentrations: up to 7% in case of hcp alloys and up to 50% for bcc alloys. [ABSTRACT FROM AUTHOR]