Silicon nanocrystals studied using Hartree-Fock and molecular dynamics

The purpose of this work is to investigate stable configurations of the nanocrystalline silicon material. Therefore, crystalline grains of columnar and spherical shape and geminate structures, formed by two adjoined grains, have been considered. The isolated grains represent the building block of the material and the geminate structures account for coalescence occurring when assembling the material. The study is subdivided into two parts. In the first part, a Hartree-Fock method at semiempirical level is applied to the evaluation of the electronic configuration of grains. These calculations show the effect of the grain size and shape on their total energy and therefore indicate stable shapes at zero temperature. In the second part, isothermal molecular dynamics is applied to the evaluation of the temperature response of the grains in the temperature range of 100-2000 K. The features of the melted materials are discussed in the light of theories on sintering and of known properties of bulk silicon.