Metallic bonding and cluster structure

Knowledge of the structure of clusters is essential to predict many-of thei r physical and chemical properties. Using a many-body semiempirical Gupta p otential (to perform global minimizations), and first-principles density fu nctional calculations (to confirm the energy ordering Of the:local minima), we have recently found [Phys. Rev. Lett. 81, 1600 (1998)] that there are m any intermediate-size disordered gold nanoclusters with energy near or belo w the lowest-energy ordered structure. This is especially surprising becaus e we studied "magic" cluster sizes, for which very compact-ordered structur es exist. Here, we show how the analysis of the local stress can be used to understand the physical origin:of-this amorphization. We find that the com pact ordered structures, which are very stable for pair potentials are dest abilized by the tendency of metallic bonds to contract at the surface, beca use of the decreased coordination: The amorphization is also favored by the relatively low energy associated to bondlength and coordination disorder i n metals. Although these are very general properties of metallic bonding, w e find that they are especially important in the case of gold, and we predi ct some general trends in the tendency of metallic clusters towards amorpho us structures.