  An iterative orbital interaction (iOI) approach is proposed to solve, in a
bottom-up fashion, the self-consistent field problem in quantum chemistry.
While it belongs grossly to the family of fragment-based quantum chemical
methods, iOI is distinctive in that (1) it divides and conquers not only the
energy but also the wave function, and that (2) the subsystems sizes are
automatically determined by successively merging neighboring small subsystems
until they are just enough for converging the wave function to a given
accuracy. Orthonormal occupied and virtual localized molecular orbitals are
obtained in a natural manner, which can be used for all post-SCF purposes.
