On the ground state structure of neutral Cun (n = 12, 14, 16, 18, 20) clusters

Density functional calculations have been performed to identify the lowest-energy isomers of Cun (n = 12, 14, 16, 18, 20) clusters using the linear combination of Gaussian-type orbitals density functional theory (LCGTO-DFT) approach. The calculations employed the generalized gradient approximation (GGA) in combination with an all-electron triple-zeta valence polarization (TZVP) basis sets. For each cluster size several hundred isomers were studied with the aim to determine the lowest energy structures. Initial structures for the geometry optimization were taken from Born–Oppenheimer molecular dynamics (BOMD) trajectories recorded at 2000 K. Several dozens structure optimizations were performed for each cluster size without any symmetry restriction. Vibrational analyzes were performed in order to characterize the optimized isomers. Structural parameters, harmonic frequencies, ionization potentials, electron affinities and binding energies are reported. The obtained results are compared with available data from the literature. This work shows that the ground state structure of the studied clusters can be assigned satisfyingly via the ionization potential and the electron affinity. The evolution of the ground state structures with increasing cluster size shows that copper clusters in the range of 20 atoms are characterized by a distorted icosahedra-like motiv.