Geometrical and electronic structure of the Pt7 cluster:: A density functional study

We present a study on the structural and electronic properties of the Pt-7 cluster by using density functional theory within the generalized gradient approximation for the exchange and correlation. The structures, relative stabilities, and vibrational frequencies of various isomers are calculated and compared with the well-studied Au-7 cluster. The ground state of the Pt-7 cluster favors a three-dimensional geometry-two-dimensional local minima are not located-whereas for its neighbor, gold heptamer, a two-dimensional geometry is favored. The most stable isomer of Au-7 is found to be an edge-capped rhombus structure and an edge-capped tetrahedron structure is found to be the most stable three-dimensional local minimum. The ground state of the Pt-7 cluster is found to be a coupled tetragonal pyramid structure with the quintet state in contrast to a pentagonal bipyramid structure obtained by semiempirical molecular dynamics calculation. The natural orbital analysis shows that the overall charge transfer is from 6s to 5d orbitals in the Pt-7 cluster, whereas in Au-7 cluster it is from 5d to 6s. The molecular orbital picture shows that the bonding orbitals are due to the hybridization between 5d and 6s molecular orbitals in Pt-7 cluster, and the nonbonding and antibonding orbitals lie close to the highest occupied molecular orbital. This may be compared with the Au-7 electronic structure, where the nonbonding and antibonding orbitals mainly consists of 5d6s hybridized molecular orbitals.