Theoretical evidence of bound metastable states in the doubly ionized nickel dimer Ni22+

Density functional theory (DFT) with generalized gradient corrections is used to study the electronic structure of Ni22+. We predict several bound metastable states, all of them having four unpaired electrons. Those states are stabilized against dissociation by a Coulomb barrier. The stability can be explained as due mainly to the interaction between the s electrons of the constituent Ni+ cations, with d8s1 configurations, that pair themselves in a bonding σ molecular orbital.