Full Cluster Expansion Theories in Fock Space

FULL CLUSTER EXPANSION THEORIES IN FOCK SPACE 

In this section, we shall motivate towards the need for a Fock-space approach to generate core-valence extensive cluster expansion theories (i.e., of type (a3)), introduced in Sec.2. Since we have to maintain size-extensivity of the energy 

Another way is to start from the precursor of the Bloch equation, eq.(6.1.15), generalized to Fock space/69,76,93/ and use the Q and P projections for the n-valence sector. Writing the Fock space Bloch equation as 

Both methods have been tried, and each has its own operational advantages. We shall classify these methods into two categories  

The various Fock space methods that we shall describe principally differ in their choice of the actual form of the cluster operator. Following the earlier analysis of Primas/29/, the form of O will be of exponential type, symbolically represented by eq.(7.1.1), but it may not strictly be exponential. There have been several choices for Ci, each having its own advantages. 

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FULL CLUSTER EXPANSION THEORIES IN FOCK SPACE 7.1 Preliminaries for a Fock Space Approach... 

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