Localized and Delocalized Orbital Basis Sets

Label Type (orthogonal) Label Type (non-orthogonal)
    AO Atomic Orbital ("the" basis set of host electronic structure system).
NAO Natural Atomic Orbital PNAO Pre-orthogonal* NAO
NHO Natural Hybrid Orbital PNHO Pre-orthogonal NHO
NBO Natural Bond Orbital PNBO Pre-orthogonal NBO
NLMO Natural Localized Molecular Orbital PNLMO Pre-orthogonal NLMO
MO Molecular Orbital (canonical; delocalized)    

*The pre-orthogonal orbitals (lacking only the final interatomic orthogonalization step of the NAO algorithm) resemble the idealized "textbook" shapes and their overlaps suggest the qualitative strength of orbital interactions.