Fast development of nanotechnologies requires a search of new methods of studying the structure and stability of nanomaterials with detailed investigation of their structural units. Computer simulations predict that silicon clusters differ significantly from the bulk crystal lattice and surface. The subject of this book is molecular dynamics simulation of noncrystalline silicon and silicon dioxide clusters with the size of 60 up to 975 atoms. It is carried out to understand features of their structure which define= their physicochemical properties. Special attention is given to the examination of stability of continuous and hollow medium-sized silicon clusters.