Dynamical stability and vibrational properties of Pt clusters

While cohesive and structural properties of Pt clusters have been widely investigated, there is scarce knowledge on their vibrational properties. In this work we investigate, by ab initio methods, the vibrational properties of Pt-n (n = 13, 19, 55, 79) clusters. We pay particular attention to the structural stability of the typical octahedral (O-h) and icosahedral (I-h) symmetric Pt-13 clusters. Their vibrational density of states (nu DOS) reveal that these geometries are magnetically unstable, while these isomers are metastable in their non-magnetic states. By performing finite-temperature molecular dynamic runs, we find that O-h and I-h clusters evolve towards layered lower energy structures. A new lowest energy isomer is thus predicted. For these Pt-13 layered clusters, and for O-h bulk type Pt-n (n = 19, 55, 79) clusters, the nu DOS and heat capacity are calculated and compared to their bulk counterparts. For the Pt-13 layered clusters we inspect and interpret, in terms of bond-order analysis, the vibrational modes for the enhanced low- and high-frequency ends of the cluster's nu DOS. We identify mostly shear, tangential type displacements for their lowest frequency modes, and mostly longitudinal, intralayer antiphase displacements for the highest frequency modes of the nu DOS.