VIBRATIONAL ANALYSIS OF NI-N CLUSTERS

The vibrational normal frequencies of Ni-n, n = 2-14, 19, 20, and 55, clusters in their most stable structure are classified using group the ory and calculated by direct diagonalization of the dynamical matrix. A Gupta n-body model potential was used to evaluate the second derivat ives of the total energy with respect to the cluster atomic coordinate s. The symmetry of the lowest-energy structures generate vibrational s pectra 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 Il) degeneraci es. Calculated frequencies for all duster sizes are lower than the dim er characteristic frequency. The width of the modes distribution and t he maximum frequency are independent of the cluster size for 2 < n les s than or equal to 55.