Variational predictability of diabatic, adiabatic or impossible diatomic states

The use of appropriately screened one-electron diatomic orbitals (OEDOs) in a variational configuration interaction (CI) of ground or excited diatomic states guarantees the nature of the desired state and speeds up the ct convergence. The method can predict, within the variational OEDOs, the possibility or impossibility of a two-centre state and can simultaneously compute both diabatic and adiabatic states. As an application, He-2(-) (4) Phi(g): (1 sigma(g)(2)1 sigma(u)1 pi(u)1 delta(g)) is shown to be impossible, and four previously unreported excited states of He-2(-) are calculated.