Density-functional-theory study of 13-atom metal clusters M-13, M=Ta-Pt

摘要

We report on the structures of six proposed global minima (GMs) of M-13 clusters (M=Ta, W, Re, Os, Ir, and Pt) and 62 isomers that are within roughly 1 eV of the GM. The GM and isomers were obtained after several global optimization runs using a first-principles (Perdew-Burke-Enzerhof exchange-correlation) method to evaluate the energy. The GM and lowest-energy isomers can be described qualitatively as amorphous and compact for Ta, W, and Pt; quasicrystalline for Re; and cubic-prismatic for Os and Ir. The icosahedron is more than 1 eV above the GM in all cases, except 0.56 eV for Ta-13. The ground-state electronic configuration of the atoms is essential to understand structural trends in the clusters. Elements with a nearly closed-shell ground-state atom (W and Pt) produce many more low-energy cluster isomers than elements with partially filled d shells, and those isomers are generally compact and amorphous. Partially filled d shells in Os and Ir lead to strong directional bonding and many 90 degrees angles between nearest neighbors. The predicted spin multiplicity of the GM is 2 (Ta-13), 1 (W-13), 6 (Re-13), 5 (Os-13), 4 (Ir-13), and 3 (Pt-13), and the spin multiplicity of all isomers within 0.5 eV of the GM is within +/- 2 of these values and is smaller than 6.