General polyelectronic systems

It was Pauling and his collaborators who generalized the Heitler-London treatment of the hydrogen molecule to general polyelectronic systems and gave the rules for evaluating the Hamiltonian matrix elements [3,4], which could also... 

We now turn to the general case. What is an appropriate functional form of the wavefunction for a polyelectronic system (not necessarily an atom) with N electrons that satisfies the antisymmetry principle First, we note that the following functional form of the wavefunction is inappropriate ... 

Tie hydrogen molecule is such a small problem that all of the integrals can be written out in uU. This is rarely the case in molecular orbital calculations. Nevertheless, the same irinciples are used to determine the energy of a polyelectronic molecular system. For an ([-electron system, the Hamiltonian takes the following general form ... 

Furthermore, note that the U-bound 4e-4o system can be thought of as a composite of two subsystems and large polyelectronic molecules are made up of many different subsystems because of operative symmetry constraints. This means, that, in general, a large part of bielectronic correlation in molecules is reproduced only at the SCF-MO-CI (VB or MOVB) level, a situation fundamentally different from the one encountered before in the case of monoelectronic polarization. 

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