Perturbation method fragmentation approach

Table 4 give the dissociation energies of each complex in its fragments and CN, evaluated in this way by the MRPT2 method. The error bar of the perturbational approach is reduced to a few kcal.mole. However, the conclusions previously obtained at the CASPT2 level, namely a decreasing stability of the MNC and MCN complexes from early to late transition metals and a possible preference for the cyanide forms in the case of median cations, like iron Fe, are still valid. 

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