Results of molecular dynamics simulations of fission reactions Na₁₀²⁺→ Na₇⁺ +Na₃⁺ andNa₁₈²⁺→ 2Na₉⁺ are presented. The dependence of the fission barriers on the isomer structure of the parent cluster is analyzed. It is demonstrated that the energy necessary for removing homothetic groups of atoms from the parent cluster is largely independent of the isomer form of the parent cluster. The importance of rearrangement of the cluster structure during the fission process is elucidated. This rearrangement may include transition to another isomer state of the parent cluster before actual separation of the daughter fragments begins and/or forming a "neck" between the separating fragments. A novel algorithm for modeling the cluster growth process is described. This approach is based on dynamic search for the most stable cluster isomers and allows one to find the optimized cluster geometries, as well as their essential formation mechanisms. Cluster growth paths for Lennard�Jones clusters have been investigated for cluster sizes of up to 150 atoms. All known global minima structures of the Lennard�Jones clusters are found.