The most stable geometries and electronic properties of gold clusters Au_n (2≤n≤20) were investigated using density functional theory with ultrasoft pseudopotentials (US-PP) and projector augmented-wave (PAW) method, based on the primary structures from genetic algorithm methods. In comparison between the two sets of results based on the local density approximation (LDA) and the generalized gradient approximation (GGA), it was found that the ground state optimal geometries were planar up to n＝6 for LDA and 13 for GGA, respectively. The calculated average nearest neighbor numbers and distances, binding energies per atom almost monotonously increase to the limits in bulk. The second differences in total energy, energy gap between the highest occupied and lowest unoccupied molecular orbitals, vertical ionization potentials and electron affinities all have odd-even alternating behavior in the range studied. The results from this study enrich the recent research work for gold clusters in both theory and experiment.

Key words: density functional theory, Au cluster, ultrasoft pseudopotential, projector augmented-wave (PAW) method