Calculation of the Electronic Factor

Definition (5) shows that TJb which is sometimes called the electronic matrix element , represents the residual interaction resulting from the overlap of the wavefunctions v /j and These functions, which describe the initial and final electronic states of the whole system, respectively, depend closely on the nature of the redox centers and of the medium, so that reliable values of T are very difiicult to obtain from ab initio calculations in complex systems. For that reason, some authors have proposed determining T b semi-empirically by using the results of spectroscopic measurements. We begin by a brief presentation of 

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Thus, relation (18) gives directly the value of lTab(Q ) as half the difference between the energies of the two stationary states /i and xJ/j, caleulated at the nuclear configuration Q = Q. We shall see in Sect. 2.2.3 some examples of theoretical calculations of the electronic factor which are based on this property. 

The preceding many-electron formulation is useful to separate the different contributions to T b, and could be easily improved to include the whole set of valence electrons of the system. However, it is not certain that this method is the most convenient for the effective calculation of the electronic factor. Actually, in the very few many-electron calculations that have been reported in the literature, Tjb was evaluated globally. These studies are summarized below. 

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