Description of Molecules in Terms of Localized Orbitals
Historically the Hartree approximation originated from the wishful conjecture that it ought to be possible to reduce the many-electron problem to a pseudo-one-electron problem with a self-consistency requirement. It was a most welcome turn of events when V. Fock succeeded in deriving the Hartree-Fock equations from the many-electron Schrödinger variation principle by constraining the solution to be an antisymmetrized orbital product, characteristic of an “independent particle model.” However, Fock also pointed out that this rigorous point of view not only leads to the novel exchange terms in the energy and the self-consistent equations but, moreover, revealed a fundamental flexibility and ambiguity in the self-consistent-field orbitals: the SCF orbitals of the pseudo-one-electron equations are not the only possible solutions of the posed problem; there exist an infinite number of different equivalent orbital sets which represent equally good and valid solution possibilities. Nonetheless, the instinctive drive towards the quasi-one-e1ectron formalism continued and, for a considerable time, Fock’s observation seems to have been repressed as a disturbing complication.
KeywordsLocalize Orbital Molecular Orbital Theory Boron Hydride Hartree Approximation Localize Molecular Orbital
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