In simulations of nuclear collisions using quantum molecular dynamics, a stable nucleus, which usually becomes unstable by emitting at least one nucleon in a few hundred fm/c, is needed. In this research, using a frictional cooling method, we obtain very stable nuclei with lifetimes up to 5000 fm/c. However, those nuclei are neither static nor in the ground; rather they show an oscillatory behavior. The frequencies of oscillation are studied and compared with the frequency of the giant monopole oscillation.