Frequencies of breathing vibrations of nearly spherical Ar clusters calculated by molecular dynamics

The breathing vibration of Ar _N cluster,N=13, 20, 25, 30 and 55, was investigated by use of the molecular dynamics method. The average distance ((bar r)) averaged over the positions of all Ar atoms with respect to the center of mass was calculated as a function of time and its frequency spectrum was derived by the Fourier transform analysis. The (bar r) value was proved to be a good index of the breathing vibration in comparison with the exact breathing vibration of an Ar dense sphere. The vibrational frequency thus estimated,f _MD, was found to increase with the cluster sizen as expected.