Density-functional study of Pt13 and Pt55 cuboctahedral clusters

The results of an accurate density-functional study of the structure and energetics of Pt-13 and Pt-55 cuboctahedral clusters are presented. The calculations utilize the Becke functional [A.D. Becke, Phys. Rev. A 38 (1988) 3098] for exchange and the Perdew-Wang functional [J.P. Perdew, Y. Wang, Phys. Rev. B 33 (1986) 12; J.P. Perdew, J.A. Chevary, S.H. Vosko, K.A. Jackson, M.R. Pederson, D.J. Singh, C. Fiolhais, Phys. Rev. B 46 (1992) 6671] for correlation, but comparison is made also with the Hartree-Fock approximation and a "hybrid" method, which employs a mixture of the Hartree-Fock and density functionals. A peculiar structural rearrangement is found for Pt-55, even imposing the cuboctahedral symmetry, which shows the tendency of the system toward "spherical" configurations. Comparison with previous atom-atom potential and extended Huckel findings shows the validity of the density-functional theory for describing the wave function of these nearly metallic systems. In contrast, the failure of the Hartree-Fock approximation on these systems is confirmed, whereas some doubts arise about the validity of the hybrid method for describing the electronic structure (if not the energetics) of platinum clusters. (C) 2000 Elsevier Science B.V. All rights reserved.