Electronic rearrangement amplitudes

The left-hand side of Eq. (177) has a structure similar to the electronic gradient vector in variational wave function calculations. Unlike variational calculations, Eq. (177) cannot be used to determine the response parameters t(n) in a CC calculation. However, for the calculation of the nth geometrical derivative W n Eq. (177) eliminates r(n), which would otherwise appear in the calculation. In fact, we show below that the calculation of (3N-6)n response amplitudes t(n) is replaced by the solution of one set of linear equations of similar but simpler structure. By inserting Eq. (176) in Eq. (177) and rearranging terms, we see that X fulfills the equations... 

However, such electron transfer can hardly be called a chemical reaction in the full sense of this term rather it is closer to the class of tunneling phenomena in the physics of solids and electronics. A chemical reaction, by definition, must include the reconstruction of molecules, the spatial rearrangement of atoms, and changes of lengths and angles of valence bonds the definition simply does not apply to small shifts over distances of the order of the zero-point vibration amplitude. 

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