Interaction Energy and Its Partitioning

The second stage corresponds to the intra-reactant equilibrium with pZ pB, while the third stage represents the global equilibrium in M with fully equalized chemical potential (electronegativity), pi = /4 = Am. which is attained after the inter-reactant B - A CT. One could also formally consider an additional stage 

let us consider the polarizational stage, M + (Q). The corresponding changes in ft and p are  

In this approach, the external potential displacements that are responsible for a transition from stage (i) to stage (ii) create conditions for the subsequent CT effects, in the spirit of the Born-Oppenheimer approximation. Clearly, the consistent second-order Taylor expansion at M°(co) does not involve the coupling hardness t A B and the off-diagonal response quantities of Eqs. (168) and (170), which vanish identically for infinitely separated reactants. However, since the interaction at Q modifies both the chemical potential difference and the 

For interpretative purposes, it is important to partition the overall electronic interaction energy B (d v, NcT), into contributions attributed to reactants A (acidic) and B (basic) in the closed M = A — B, or to their constituent fragments. Following Eq. (175), we consider separately the (electrostatic + polarization) - energy, /VCT = 0) = ES + EP = (M +) — (M°), and 

The first part can be naturally partitioned into the reactant contributions  

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