Quantum chemical simulation of silicon nanostructures

The point defects in silicon, their migration, geometry and electronic structure, as well as some models for nanowires, were studied. The ab initio Self Consistent Field Molecular Orbital method and the molecular cluster model were used. Hydrogen pseudoatoms were used to saturate dangling bonds of the cluster. The influence of the compression onto defect structure and properties was simulated by changing the bond length value. The silicon interstitial migration activation energy, calculated as the difference between the total energies of the cluster with interstitial in tetrahedral and hexagonal positions, is 4.21 eV, and it does not depend on local pressure. The influence of high pressure simulated by uniform lattice compression is shown to reduce the role of the chemical interaction and to enhance the role of physical repulsion. This is manifested as a shift of the oxygen interstitial migration pathway towards the free volume. The electronic structure of silicon interstitial was studied. The structure and stability of nanowires in silicon and carbon were discussed, and the break of symmetry at 0.165 nm distance between the carbon atoms was found.