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66 C. VALDEMORO
These results show that at least for the ground state, the correlation effects described
by the term are overestimated in the IP and MPS calculations.
4.3.3. Other applications
Before concluding this section, it must be pointed out that there are other fields of
application of the SRH formalism. Thus, Karwowski et al. have used it in the study
of the statistical theory of spectra [30,38]. Also, the techniques used in developing the
p-SRH algorithms have proven to be very useful in other areas such as the nuclear
shell theory [39,40].
We think that the physical meaning of the SRH matrices is not yet fully understood
and can therefore be considered an open field of research. It is to be expected that a
more complete understanding of the SRH matrices will lead to new applications of
this formalism.
5. The Contracted Schrödinger Equation
In this section I will outline a new line of research recently initiated by our group. It
must be emphasized that the only points in common with the SRH formalism pre-
viously described are that no call is made upon the N-electron WF of the electronic
system and that its basic formal tools are also the MCM and the RDM's.
5.1. THE NAKATSUJI AND COHEN-FRISHBERG EQUATION
The integration with respect to N – q electron variables of the Schrödinger equation
was reported simultaneously by H. Nakatsuji [41] and by L. Cohen and C. Frishberg
[42] in 1976. The form of this equation (NCF) for q = 2 is:
