D System with Direct Correlations Only

The description of the two-state system,/= 2, was introduced earlier in Sections 7.1 and 7.2. Here, we present some quite obvious results for systems with nn direct interactions only. Since we discuss only a restricted group of events, we use a simpler notation for the correlations. Thus, instead of g(sj = a,S2 = P), we simply use g 2) or gi2(2) to denote pair correlations (between the event site i occupied and site i + 1 occupied ). Also, we shall always refer to the X. 0 limit as the correlation and omit specific notation for this limit. 

For higher-order correlations, the particular correlation depends on m and on whether the chain is open or closed. For instance, when m = 3 

All these can be read directly from the number of bonds between the ligands. The situation is far more complicated when indirect correlations are operative, as we shall see in the next section. 

The behavior is quite different for the cyclic closed system. Here, as can be seen from Fig. 7.2b, the location common to any m and is 

The different behavior of the open and closed system is due to the difference in the pattern of correlations in the two systems hence the average correlation differs for the two systems with the same m. 

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