Bond-Length and -Energy Variation of Small Gold Nanoparticles

The relations between the bond energy, bong length and coordination number of Au nanoparticles of 2.7 similar to 5.5 nm have been studied by molecular dynamics simulation method. It is shown that the bonds contracts only in the 1.5 times atomic diameter in the surface, but the bond length are the same as the bulk in the core of particles. The present results are well consistent with the recent experimental values. It is also found that the bond energy increases with the decrease of coordination number. Between 1 and 1.5 times atomic diameter in the surface, the bond length contracts but the single bond energy keeps invariant. Thus the structure of a nanoparticle can be classified as three regions, i.e., the surface, the subsurface and the core. The core is the same as the bulk, the surface structure is formed by the coordination number imperfection, and the subsurface can be regarded as the transitional shell from the core to the surface. It is also concluded that the increase of bond energy results from the coordination number decreasing, and the bond energy contraction is from the minimum of total energy.