Vibrational analysis of clusters

The vibrational normal frequencies of (Formula presented), n=2-14, 19, 20, and 55, clusters in their most stable structure are classified using group theory and calculated by direct diagonalization of the dynamical matrix. A Gupta n-body model potential was used to evaluate the second derivatives of the total energy with respect to the cluster atomic coordinates. The symmetry of the lowest-energy structures generate vibrational spectra with strong (n=13, and 55), medium (n=4 and 6), weak (n=3, 5, 7, 8, 10, 12, 14, 19, and 20), and null (n=9 and 11) degeneracies. Calculated frequencies for all cluster sizes are lower than the dimer characteristic frequency. The width of the modes distribution and the maximum frequency are independent of the cluster size for 2 <n ≤55. © 1996 The American Physical Society.