TATO-DMM AND INTERSUBSYSTEM FRONTIER

The variations of the one-electron densities 6Pria with a = a, ,v,( and the polarity (/ — P[l) of the bond with m = 1 deserve some discussion. As it is seen from eqs. (3.86), (3.105) each bond incident to an atom contributes an increment to the quasitorque and to the pseudotorque acting upon its hybridization tetrahedron. In the equilibrium these increments separately sum up to zero. We can think that the equilibrium shape and orientation of the hybridization tetrahedron is obtained within a TATO DMM model applied to the entire system. Then, within such a model, there exists an atom corresponding to the left end of the bond with m = 1 having number Li according to our previous notation. The HOs obtained in this approximation provide an initial guess for HOs in the system including those of the atom Pi, which 

These additional pseudo- and quasitorques produce the pseudo- and quasirotations of the hybridization tetrahedron of the boundary atom R. In the linear response approximation, it corresponds to the treatment of the corresponding pseudo- and quasitorques by the fV7/0 1 matrix which is simple (diagonal in the basis of the and SAi variables) in the case of symmetric hydride  

Analogously, torques acting upon the atoms Lm (the left-end atom for the m-th bond) with to 2, which are neighboring to the boundary from the MM side, arise due to variation of the shape of the hybridization tetrahedron  

The MM subsystem in its turn also affects the parameters of the QM subsystem as any geometry variation in the MM subsystem induces changes in pseudo- and quasirotation angles defining hybridization of the frontier atom. The corrections to the QM one-center Hamiltonian parameters (in the linear approximation) are  

The resonance integrals in the QM subsystem are also modified. In the respective DCFs the corrections can be expressed as  

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