Systematic study of the lowest energy states of Aun (n=1-4) using DFT

A density functional theory study of Au, Au2, Au3, and Au4 is performed focusing on the study of gold tips or contacts of interest in investigations of molecular-scale electronics. The ground state for the four systems corresponds to the one with the lowest multiplicity, and the ordering of energies follows the multiplicity in all cases. It is found that the tetrahedral geometry of Au4 is not the preferred one for the lowest spin states with neutral charge, but is the preferred one for charged systems. The ionization potential and electron affinities for the four systems were also obtained. A qualitative interpretation of the Kohn–Sham highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) orbitals is given based on the present calculations.