Correlation into an Approximate Wave Function

Inclusion of Correlation into an Approximate Wave Function 

We now turn to the last of the three general questions raised in Section 1. If we are going to perform calculations beyond the Hartree-Fock theory, we have to decide whether or not we are to proceed via the SCF approximation. Before discussing the methods themselves, we shall examine the computational side of the problem. 

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The counterpart of the problem of determining the correlation content of a wave function is, of course, the problem of including correlation into an approximate wave function. Putting aside strictly technical details, there remains the question whether the SCF treatment is an essential step in a refined calculation. If one by-passes the SCF step, the genuine definition of correlation becomes inapplicable, unless one performs separately an independent-particle calculation. Both procedures... 

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