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The four-component Au-Cu-Pd-Pt nanosystems of different sizes with the stoichiometric composition Au3CuPd12Pt4 were studied. The molecular dynamics method was used as a simulation method, the interatomic interaction was described by the tight-binding potential. Based on the results of a series of computer experiments, it was found that the four-component Au-Cu-Pd-Pt nanoparticles do not have a tendency to form a core-shell structure, even though gold atoms demonstrate an increased segregation to the surface. Melting and crystallization temperatures were determined for the studied Au-Cu-Pd-Pt nanoparticles. The dependence of the crystallization temperature on the cooling rate was also established. With an increase in the cooling rate, the crystallization temperature decreases, and the temperature range in which crystallization occurs increases, while the heating rate does not significantly affect the melting temperature. It is shown that the size effect and the effect of the temperature-changing rate make it possible to control the dominant presence of the fcc or hcp local structure, and also affect the temperature stability of the resulting crystalline phases.

The reliability of the atomistic simulation is determined in terms of the correctness of the problem statement, including the choice of the interatomic interaction potential and its parameterization. In this paper, a detailed testing of the tight-binding potential parameters was carried out by means of studying the influence of the ratio between pair and many-body interactions on the process of the structure formation in binary Pd-Pt nanoparticles. Three parameterizations of the tight-binding potential for the cross parameters were selected: set (I) corresponded to the use of the Lorentz-Berthelot rule, sets (II) and (III) specified the scaling laws for the pair interaction parameters and the many-body interaction parameters, respectively. For sets (I) and (III), the surface segregation of palladium atoms was established, while the use of set (II) led to the formation of the Janus structure. In addition, differences in the formation of the local structure in binary Pd-Pt nanoparticles were established. Set (III) predicts the dominance of the local bcc structure. Radial distributions of the local density of Pd and Pt atoms in the Pd-Pt nanoparticles at a final temperature of 300 K were also calculated.

The problem of the thermal stability of mono- and binary metallic nanocages consisting of gold and silver atoms with the same nuclearity of 3000 atoms is considered. The initial configurations of nanocages were obtained in the ClusterEvolution software by cutting them out of a larger icosahedron. The heating process for studying the thermal stability/instability was simulated in the Metropolis software using the Monte Carlo method and the Metropolis scheme. The interatomic interaction was described by the tight-binding potential. The influence of the composition, characteristic dimensions (inner and outer radii), and the shape of the inner surface in the initial configuration on the thermal stability of nanocages was studied. The temperature of complete collapse of the internal cavity of nanocages was determined. The results of calculations of the temperature dependence of the average local density and the local density profiles at different temperatures corresponding to different initial configurations, as well as the temperature evolution of the fractions of crystalline structures in them, are presented and analyzed.

The article is devoted to the study of stability of ternary Cu-Fe-Ni nanoparticles (consisting of 5400 atoms) with a core-shell structure and its relationship with the surface segregation. The main focus is on modeling their structural formation using the LAMMPS software. The authors test the hypothesis that stability of nanoparticles depends on the spontaneous segregation of one of the components to the surface. Three configurations with different atomic distributions (configuration Cu45Fe45Ni10 with random distribution of atoms, as well as configurations – Cu25Fe25@Ni50 and Fe25Ni25@Cu50) are considered, and numerical modeling is performed for each of them using molecular dynamics methods and applying the tight-binding and embedded atom method potentials. The analysis showed that copper tends to segregate to the surface, while nickel concentrates in the core, significantly affecting mechanical properties of the nanoparticles. Patterns of the defect formation and their impact on the strength of nanostructures were identified. The article emphasizes that the correct choice of shell and core can both stabilize and destabilize the nanoparticles, providing prospects for the practical application of these materials.

The processes of the structure formation in Ti-V binary nanoparticles and the factors influencing the crystallization process are discussed. The objects of study were Ti-V binary nanoparticles containing N=200, 400, 800, 1520, 3000, and 5000 atoms with various compositions. The computer experiment was conducted using the molecular dynamics method. Interatomic interactions were described using the tight-binding potential. Based on a series of computer experiments, it was determined that the crystallization process of Ti-V binary nanoparticles is significantly dependent on both their size and component ratio. As the size of the nanoparticles increases, the crystallization temperature rises, and the component ratio has a substantial influence on the formation of crystalline phases. The lowest crystallization temperatures were observed at titanium-to-vanadium ratios of 25-75% and 50-50%. Larger nanoparticles also exhibit pronounced phase segregation, with FCC and HCP phases dominating depending on the titanium-to- vanadium ratio. The observed tendency to form a multilayered onion-like structure indicates a more complex structure formation process than surface segregation.

Scenarios of structure formation in four-component nanoparticles are considered. The objects of study were Au-Cu-Pd-Pt nanoparticles containing N = 400, 800, 1200, 1600, 2000, 4000 atoms of the stoichiometric composition Au3CuPd12Pt4. Two alternative modeling methods were used: the molecular dynamics and the Monte Carlo. The interaction between atoms was described by the tight binding potential. The phase transition temperatures for the nanoparticles under study were determined. It has been established that the melting and crystallization temperatures depend both on the size of nanoparticles and on the rate of temperature change (by using the molecular dynamics method). The melting rate of nanoparticles has little effect on the melting temperature, while increasing the cooling rate significantly reduces the crystallization temperature and slows down the segregation processes. The process of coalescence of two four-component nanoparticles was modeled. During the process of coalescence, significant mixing of atoms of different types does not occur when using the Monte Carlo method, which leads to some stopping of the growth of the neck at the point of contact, in contrast to molecular dynamics method, where the growth of the neck occurs gradually.

The processes of structure formation in Co-Au and Ti-V metal nanoparticles as well as factors affecting the crystallization process are considered. The objects of the study were Co-Au and Ti-V binary nanoparticles containing N = 400, 800, 1520 and 5000 atoms with the equiatomic composition. The computer experiment was carried out using method of molecular dynamics. The interatomic interaction was described by the tight-binding potential. According to the results of a series of computer experiments, it was found that the main factors influencing the possibility of obtaining crystalline phases are: the cooling rate of binary nanoparticles, their size and the size mismatch of atoms included in the composition, as well as the nature of the interaction of metal atoms. The manifestation of stability/instability in binary nanoparticles may be due to patterns of formation of crystalline phases. Moreover, the tendency to segregate one of the components in a binary system may not be the main factor determining the stability/instability of such a system.

The melting and crystallization phase transitions in the five-component metallic Au-Ag-Cu-Pd-Pt equiatomic nanosystem were investigated. The complex approach to atomistic modeling is due to the use of alternative methods of computer simulation – the molecular dynamics and Monte Carlo methods. The interatomic interactions were described by the tight-binding potential. According to the results of a series of computer experiments, it was established that five-component nanoparticles of equiatomic composition can form crystalline phases during cooling. Melting and crystallization temperatures for the investigated five-component nanoparticles were determined. The values obtained by alternative methods are in good agreement. For five-component nanoparticles, the concept of fixing the temperatures corresponding to the beginning and end of the phase transition process is confirmed. The metals that make up five-component nanoparticles, the atoms of which in the process of crystallization form the central part of the nanoparticle (core) and the peripheral regions, including the surface of the nanoparticle, are determined.

This work is devoted to the problem of thermal stability of mono- and binary metal nanocages consisting of gold and silver atoms. The number of atoms in the studied nanocages was 1744, 2150, 2470 and 3370 atoms. The characteristic size (outer diameter) of nanocages is from 4,4 to 5,1 nm. Interatomic interaction was described by the tight-binding potential. Analysis of the caloric dependences of the specific potential part of the internal energy made it possible to identify the temperature regions of «healing» of cavities (pores) on the faces and in the internal regions (cores) of nanocages. An example of the structural collapse of a nanocage is described in detail, as a result of which crystalline and quasicrystalline phases are identified in the nanoparticle core for a temperature corresponding to melting for the chosen size. Segregation in a binary Au-Ag nanocage before and after its collapse was also studied.

In this work, bimetallic Cu-Ag nanoparticles of five stoichiometric compositions of various sizes were studied by molecular dynamics method using a many body EAM potential. Regularities of the structure formation are established, their characteristic features are described. In particular, in compositions with 10, 70, and 90 at.% Cu content, after the melt cooling, typical fcc structures with intersecting atomic planes of the hcp phase are formed. In compositions of 30 and 50 at.% Cu, the fraction of identified phases does not exceed 20% of the total number of atoms. A tendency to the formation of a core-shell structure was revealed in the case of a high copper content, while in the case of a high silver content, a so-called onion structure is formed. Using the caloric curves of the potential term of the internal energy, the melting and crystallization temperatures were determined. It has been established that the concentration dependences of the melting temperature of bimetallic Cu-Ag nanoparticles have a minimum corresponding to the equiatomic composition for all sizes. For the crystallization temperature, both the concentration dependences and the size dependences are less pronounced, but the minimum value of the crystallization temperature also corresponds to the equiatomic composition for all sizes; with an increase in the size of bimetallic Cu-Ag nanoparticles, a slight increase in the crystallization temperature is observed.

Various types of configurations of the Au-Cu-Pd-Pt four-component nanosystem, including complex core-shell structures, have been studied. The Monte Carlo method was used as a simulation method, the interatomic interaction was described by the tight-binding potential, i.e. the Gupta potential. According to the results of a series of computer experiments, it was found that four-component nanoparticles of this system do not tend to form a core-shell structure, even though gold atoms have an increased surface segregation. The melting temperatures for the nanosystems under study have been determined. The obtained values are in the range from 1100 K to 1250 K and weakly depend on the composition of nanoparticles (the ratio of the number of atoms). A stoichiometric composition based on these metals was found, for which, during cooling, an FCC crystal structure with inclusions of the HCP phase is formed. However, no distinctive features in the nature of segregation for this stoichiometric composition have been established. All considered stoichiometric compositions in the studied temperature range were stable with respect to decomposition.

This work studied bimetallic nanoparticles Ni@Ag and Ag@Ni with the total number of atoms 4000 by the molecular dynamics method using the tight-binding potential. The pattern of segregation and structural formation is established and its characteristics are described. Based on the analysis of the behavior of the calorie curves of the potential part of the internal energy, the melting and crystallization temperature was determined. The data obtained suggest that the processes of segregation in Ni@Ag and Ag@Ni nanoparticles are associated with the nanoparticle stability. The silver shell loses its stability above 900 K, while the nickel core remains solid and retains its structure. At the same time, in Ni675@Ag3325 nanoparticles the processes of the surface segregation of the nucleus atoms were less pronounced, whereas in Ag675@Ni3325 nanoparticles silver atoms actively segregated onto the surface of the nanoparticle. The features and fundamental differences in the processes of melting and crystallization of these nanosystems, as well as the temperature ranges of their stability, are analyzed. The relationship between the degree of intensity of segregation processes of nanoalloys during modeling and the stability of these systems is shown.

In this work, of the structure formation was investigated using Au-Ag, Ti-Al, Ti-V bimetallic nanoparticles as the patterns. These bimetallic nanoparticles have different atomic size mismatches and different crystallization temperatures. A series of molecular dynamics experiments was carried out. Based on their results, the final configurations with the lowest energy were analyzed and the concentration dependences of the mixing energy were obtained. An analysis of the concentration dependences of the mixing energy makes it possible to predict the compositions and sizes of bimetallic nanoparticles, which can exhibit instability, such as for Ti-V bimetallic nanoparticles. The asymmetry of individual concentration dependences of the mixing energy is evidence of specific structural transformations characteristic for the given composition and size. It has been established that structural segregation is characteristic for Au-Ag, Ti-Al bimetallic nanoparticles and it is actively manifested at low concentrations of a more low-melting component. The competing phases in this case are fcc and hcp phases. In addition, for the average sizes considered in the article, the dependence of the crystallization temperature on the composition of bimetallic nanoparticles was investigated.

This work studied bimetallic Au-Co nanoparticles of three stoichiometric compositions of various sizes by the molecular dynamics method using the tight-binding potential. The regularities of structure formation are established, their characteristic features are described. In particular, in compositions with 50 at% and 75 at% Au content, multiple small nuclei of local icosahedral symmetry are formed. Crystalline phases prevail only in the Co -25 at% Au composition with an increase in the particle size. Compositions are revealed in which the internal symmetry of a nanoparticle is determined by the presence of one icosahedron or a superstructure of several icosahedrons. The concentration dependences of the mixing energy of a bimetallic Au-Co nanoparticle are calculated. It is shown that there are concentrations of compositions at which bimetallic nanoalloys can exhibit instability in a certain size range. Crystallization temperatures were determined using the caloric curves of the potential part of the internal energy. It was found that the crystallization temperature demonstrates a moderate or significant, depending on the composition as well as growth with an increase in the size of bimetallic Au-Co nanoparticles.

The architecture and software Metropolis for computer simulation by the Monte Carlo method, as well as its modifications, are described. The tight-binding potential that does not exclude the possibility of using other modifications of many-body potentials. In comparison with previous software implementations of the Monte Carlo method, this modification has increased the rate of calculations by 700 times for a selected nanoparticle size. The data on the convergence of the results of modeling by the Monte Carlo method are presented on the example of the melting point. The developed software package is constantly tested for calculations of various mono- and multicomponent nanoparticles and nanosystems. The results obtained show fairly good agreement with other numerical methods, primarily molecular dynamics, and real experiment. Further development of the software package and its performance indicators are planned to be improved using parallelization of computations and the use of computing technology on graphics processors CUDA.

Combination of experiment and computer simulation made it possible to study the features of the process of Cu — Ni nanoparticle synthesis. Nanoparticles are synthesized by the method of exothermic combustion in solutions. The X-ray phase analysis of the obtained materials showed that all samples are pure bimetallic nanopowders with a distorted cubic crystal structure of each metal. The Monte-Carlo method in the temperature range from 300 to 600 K established regularities of the neck formation for two cases of the initial location of copper and nickel nanoparticles: direct contact and relative displacement by 0,2 nm. The possibility of close integration of crystal structures as a Cu and Ni nanoparticles interaction result is shown.

Exemplifying on two bimetallic nanoparticles Cu — Pt and Au — Ag, the internal structure and external surface has been investigated in the process of dealloying. Equiatomic compositions with the total number of atoms Ntot = 3000 are considered. In the dealloying process half of both the copper and silver atoms were removed. The Monte Carlo method within the Metropolis scheme is used as a simulation method. The interatomic interaction was described by the tight-binding potential. As it was expected, the selective corrosion leads to the fact that the surface layer of the particle is enriched with one of the components atoms. However, the particle core retains the structure of the binary nanoalloy. We also found that as a result of the selective corrosion, a defective structure of the nanoparticle is formed. Accordingly, we assume that it is these defects (mainly vacancies) that lead to the porous structure of larger binary nanoparticles observed in experiments on the dealloying. A change in the specific surface area per unit volume or weight affects the adsorption and catalytic properties, as well as the corrosion resistance of bimetallic nanoparticles.

In this work, molecular dynamics simulation is carried out of crystallization of bimetallic Co — Au nanoparticles from the melt with various compositions. The effects of the dimensional mismatch between the atomic radii and external pressure on the final configurations cooled up to the temperature 100 K was studied. It was found that the specific potential energy for the bimetallic Co — Au nanoparticle increases with an increase in external pressure. Besides, as the external pressure increases, structural changes occur, namely, the average number of icosahedral atoms inside the cluster changes in a nonlinear character. The dependence of the specific potential energy of bimetallic Co — Au nanoparticles of various compositions on the coefficient of the dimensional mismatch ξ is more complex. The minimum for the gold-enriched composition and equiatomic composition is observed at the values ξ = 1,09 and ξ = 1,15, respectively.

Two alternative molecular dynamics models (programs) involving the Gupta (tight-binding) potential have been used to reproduce the dealloying phenomenon in the Au – Ag nanoalloy. Program I successively removes Ag atoms from the particle surface layer (we simulated nanoparticles consisting initially of 1500 Au and 1500 Ag atoms). Program II proposes search and removing atoms with lowest specific binding energies. We have found that as a result of dealloying the particle surface layer is really enriched with Au atoms. However the particle core keeps in general the structure of the initial nanoalloy. We have also established that dealloying results in formation a defected particle structure (vacancies, first of all). Presumably, just such an effect yields the porous structure of bigger Au – Ag particles in laboratory experiments on dealloying.

On the basis of the molecular dynamics results obtained by using the tight binding potential, the heats of melting, crystallization, and also the sublimation and evaporation heats of platinum and palladium nanoclusters were found. The obtained size dependences are linear if the inverse radius is chosen as an argument, which allows extrapolating the dependencies to the corresponding bulk phases and comparing with the tabulated values.

In this work, we performed atomistic modeling of the behavior of Co (core) – Au (shell) and Au (core) – Co (shell) during thermal exposure in order to study the stability/instability problem for the above nanostructures using the tight binding potential and two alternative computer programs based on the molecular dynamics and Monte Carlo methods. It has been shown that both the Co (core) – Au (shell) and Au (core) – Co (shell) structures can be stable. However, molecular dynamics results predict a short-term decay of Au2500 (core) / Co2500 (shell) nanostructures in a high-temperature region followed by a self-assembly, while the Monte Carlo method predicts the appearance of defects – cavities in the particle core and on the boundary between two components. It is concluded that the size effect can be the main factor determining stability/instability for the Co (core) – Au (shell) and Au (core) – Co (shell) structures.