The gross physical behavior of solids and liquids is the result of atomic or molecular reactions to external forces. Using molecular dynamics, we can study such reactions in the small, on the molecular level. In quasimolecular dynamics, molecules are aggregated into larger units, called quasimolecules, in order to simulate behavior in the large. Mass and energy conservation considerations are fundamental in this approach. In particular, we will simulate the generation of cracks in a slotted plate which, for illustrative purposes, is chosen to be of pure copper. CRAY X—MP/24 supercomputer examples are described and discussed.