Electronic description using both localized and delocalized orbitals: application to a transition metal system

A method for an accurate treatment of the electronic correlation in multi-reference systems using localized orbitals has been recently proposed. However, for some systems, the physics impose that they cannot be described only from local contributions. In that case, it is impossible to use only localized orbitals. The particular example presented here concerns the study of a chain of transition metal atoms (nickel and copper). It appears that the d orbitals may be kept local, while the s electrons are described by orbitals that are delocalized on the whole shape of the molecule.