First-principles Studies On The Structures And Electronic Properties Of Gold Clusters

Clusters are the agglomerates of a few to a few thousand atoms with relative stability and with a radius smaller than 50 nm. Clusters are the borderland between the microscopic single atom and the macroscopic solid state exhibiting many extraordinary properties, for example, electronic shell structure and band structure exist at the same time, the stability of magic number, quantum size effect et. Thus one can design new materials using clusters as the building blocks. Gold nanocluster have a potential application as building block for functional nanostructure materials, electronic devices, and nanocatalysts. But the experiment synthesized is inefficient and hard separated and the information of experiment is lack, so the extensive studies on the gold clusters become the hot topic up to now.Structural evolution and electronic propertires of medium-sized Aun (n=29-42) clusters have been explored using an extensive, unbiased search based on density functional theory and genetic algorithm methods. The density functional calculations were conducted using the Accelrys Dmol3 code. All calculations involved used the generalized gradient approximation (GGA) functional by Perdew-Burke-Ernzerhof functional (PBE). A relativistic semi-core pseudopotential (DSPP) and the'double numerical plus polarization'(DNP) basis set (a polarized split valence basis set of numeric atomic functions) were employed. We denoted this scheme as PBE/DSPP/DNP.The structural evolution and competition between the hollow cage, amorphous, fcc-like and tubular structures for medium-sized Aun clusters in the size range of n=29-35 were investigated using density functional theory. The most stable structure of Aun (n=29-32,42) is the hollow cage structure, and Aun (n=33-41) adapt amorphous structure. The transition of the most stable structure from hollow cage to amorphous packing occurs at Au33. The amorphous has a higher average coordination number. We have found that the hollow cage and amorphous structure exhibit a strong competition.The dependences of binding energy per atom (Eb), highest occupied and lowest unoccupied molecular orbital energy gaps (HOMO-LUMO Gap), vertical ionization potentials (VIP) and partial density of states (PDOS) are studied in detail. The binding energy per atom increas as the atom size grows.The Au31, Au32 and Au34 possess the higher HOMO-LUMO Gap and vertical ionization potentials.The present results provide useful insight into understanding the structural evolution and electronic properties of neutral Au clusters. The gold clusters considered here give some useful information for the experimental further studies.