Theoretical Study of the Structures and Stabilities of Small CaCn, CaCn+, and CaCn-(n= 1−8) Cyclic Clusters

Abstract

CaCn, CaCn+, and CaCn- (n = 1−8) monocyclic clusters have been studied using the B3LYP density functional method. Predictions for several molecular properties that could help in possible experimental characterization, such as equilibrium geometries, electronic structures, dipole moments, and vibrational frequencies, have been reported. For the CaCn monocyclic clusters, the electronic ground state is found to be a singlet for n-even clusters, whereas in the case of n-odd, singlet and triplet states are predicted to lie very close in energy. Both anionic and cationic clusters have doublet ground states, with the only exception of CaC3+ that has a 4B1 ground state. An even−odd parity effect, with n-even clusters being more stable than n-odd ones, is found for both neutral and anionic species, whereas in the case of cationic species this effect is slight and reversed. Ionization potentials exhibit also a clear parity alternation trend, with n-even clusters having larger values than n-odd ones. In the case of the electron affinities, a slight variation is found. It is also predicted that all neutral clusters prefer cyclic arrangements, with cyclic isomers being more favored for n-even clusters. Monocyclic ground states are also predicted for the first members of the series in the case of anionic and cationic monocyclic clusters.