[en] Key words: tight-binding method; molecular dynamics simulation; clusters; silicon; cohesive energy; nondiamondlike and diamondlike structure. Subjects of inquiry: structure and energetic properties of nanosized silicon clusters. Aims of inquiry: systematical quantum-chemical simulation of nanosized silicon clusters for establishment of changing structural and energetic characteristic regularities with increasing cluster size. Method of inquiry: computer simulations; self-consistent non-conventional tight-binding method; molecular dynamics method. The results achieved and their novelty. First systematical simulation of structure and stability of silicon cluster contained up to 61 atoms during the process of growth has been studied using non-conventional tight-binding method. Their cohesive energies, ionization potentials and electron affinities have been calculated. A new growth pattern of silicon clusters having quasi-one-dimensional structure with a period of six atoms and unit cell in the form of a pentagonal pyramid in the range of sizes from 8 to 61 atoms has been revealed. The structural cluster distortions conditioned by accumulation of strains in the bonds between atoms along the central axis have been discovered. As a result one end of the clusters has converted into two-dimensional structure. Impact of models of surface reconstructions (dimerization and trimerization of surface bonds, overcoordination of surface atoms and removal of low-coordinated atoms) of diamond-like silicon clusters Si29, Si38, Si59 on their internal structure have been shown. The diamond-like core remains only in the case of dimerized (trimerized) surface. The most stable clusters maintain pentagonal pyramids on their surface. Comparative analysis of structural and energetic properties of quasi-one-dimensional and diamond-like clusters has carried out. A lower bound of 115 atoms for the transition from the non-diamond-like to diamond-like structure has been estimated by extrapolation method. Practical value. The obtained results noticeably contribute to development of understanding structure and properties covalent nanoparticles, growth mechanisms and role of surface reconstructions of nanoparticles for fundamental nanotechnology base. It can be taken into consideration at synthesis of nanoparticles for intentional production of nanoparticles with necessary properties. Degree of embed and economic effectivity: The work is of pure fundamental significance and its results can be used in the field of theory of nanoparticle structures and processes of their growth. Sphere of usage: condensed physics; nanoscale systems. (author)

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[en] Molecular-dynamics (Md) simulations with forces derived directly from electronic structure calculations have now become a valid research tool in the condensed matter physics. These simulations are very efficient when combined with the semi-empirical electronic structure calculation methods such as tight-binding (TB) ones. To this aim a number of tight-binding electronic structure and total energy calculation methods have been developed so far and in wide used for MD simulations of solids, atomic clusters, surfaces, and defects. However, the range of systems and phenomena for which these methods can be reliably applied is very restricted yet. This is due to, at least, two reasons. The first, these methods introduce a large number of fitting parameters that have no definite physical meanings and cannot be related with chemistry of interacting atoms, requiring a large database for their fitting, which is mostly incomplete or inaccessible. The second, a number of fundamentally and practically interesting systems such as surfaces, interfaces, defects in solids, and clusters of atoms (nano-structures) can not be adequately treated without self-consistent account for charge distribution in a system. One of the most challenging problems in this respect is the state (position in a lattice) and motion (diffusion, migration) of defects and impurities, as well as their interactions and electrical levels in semiconductors, which are strongly dependent on charge states of defects and impurities. However, the TB practitioners have not paid much attention to these issues, exploiting sometimes a Hubbard-like term only in order to prevent unphysical charge transferring between atoms. This paper presents development of tight-binding molecular dynamics approach based on the combination of the self-consistent tight-binding method of new generation and new more accurate integration algorithm of Newtonian equation of motion and its application to number of fundamental defects and impurity-defect interactions in silicon

[en] With using the quantum-chemical tight binding method the stabilities of hollow silicon clusters are investigated in the process of quasi-one-dimensional growth. The obtained hexagonal structures of clusters Si₂₄ and Si₂₆ can be the 'building units' of a silicon nanowire. (authors)

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[en] A fragmentation of small stoichiometric gallium-arsenic clusters stimulated by Auger-ionization of atomic inner shells has been investigated by computer simulation method. Auger-ionization may be, for example, in laser field or at absorption of X-rays. The self-consistent tight-binding electronic and total energy calculation method and new algorithm for integrating the Newtonian equations are used for simulation of cluster fragmentation. It is shown that two-electron ionization of Ga₂As₂ cluster makes it unstable and cluster distorts on three parts - two Ga⁺ ions and As₂ molecule. (author)

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