Theoretical study of the icosahedral to cuboctahedral structural transition in Rh and Pd clusters
CEA/Saclay, DSM/DRECAM/SRSIM, 91191 Gif-sur-Yvette Cedex, France
2 Laboratoire de Physique des Solides, Université Paris Sud, 91405 Orsay, France
Published online: 15 September 2000
The icosahedral to cuboctahedral structural transition in RhN and PdN clusters with closed atomic shells and increasing sizes (N=13, 55, 147, 309, 561) is studied using a tight-binding description of the valence band including sp electrons as well as d electrons assuming an homogeneous relaxation, the effect of inhomogeneous relaxation being discussed by means of an empirical potential. The critical size at which the cuboctahedral and icosahedral clusters have roughly the same energy is similar for Rh and Pd. The potential energy profile for the Mackay transformation which distorts continuously a cuboctahedron into an icosahedron is also calculated. The cuboctahedral structure is found to be unstable for N=13 but, for 55 ≤ N ≤ 561, the potential energy profile exhibits an activation barrier which is expected to persist at least in some range of larger sizes. This explains the coexistence of both geometries at intermediate sizes. Finally the electronic structure of these clusters is also discussed.
PACS: 36.40.Ei – Phase transitions in clusters / 71.24.+q – Electronic structure of clusters and nanoparticles / 71.20.Be – Transition metals and alloys
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2000