We investigate, by molecular dynamics simulations, the structural behavior of silicon  nanoparticles of sizes N ranging from 4 to 20 atoms. The interaction between silicon atoms is modeled by the EDIP potential (Environment Dependant interatomic Potential) which takes into account the tetravalent character of silicon as well as the covalent type of its chemical binding. EDIP potential is well known for its reliability in reproducing correctly the bulk silicon properties. In the present contribution, we use it for silicon nanoparticles of relatively small sizes, in the aim to estimate the deviations with regard to its approach for a nanoscopic system. Two sets of simulations have been carried out, for the whole range of sizes, starting each one from a different atomic initial configuration: (i) fragment of the diamond structure since silicon crystallises in this structure and (ii) atomic closed shells. The energy curves reveal that for N<9, the second initial configuration produces more stable structures than the first one. On the other hand, a dominant tendency to icosahedral structures is observed, above a certain size, for all the nanoparticles resulting from the two initial configurations. A third set of simulations is carried out by starting, for each size, from the most stable configuration resulting from the two previous sets of simulations. In this set, a simulated annealing followed by a quenching to the temperature of 1K is performed in order to approach the global minimum structures (optimization algorithm). Thus, the latter set of simulations is supposed to generate the most stable structures. However, some exceptions have been found out for some particular sizes (N=5, 6, 11, 15, 16, 17 and 20). Our finding are compared to both experimental and computational results available in the literature for the same nanoparticles.

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