Minimum energy path avoidance

G. OH + CH3F Avoiding the Minimum Energy Path The reaction... 

Figure 2 Topological relation between an avoided crossing and a conical intersection (Cl). The avoided crossing is the cross section through the cone along R-P. The minimum energy path is R-CI-P and passes through the apex of the cone.

In many cases, it is also helpful to have the path repel itself so that the transition pathway is self-avoiding. An acmal dynamic trajectory may oscillate about a minimum energy configuration prior to an activated transition. In the computed restrained, selfavoiding path, there will be no clusters of intermediates isolated in potential energy minima and no loops or redundant segments. The self-avoidance restraint reduces the wasted effort in the search for a characteristic reaction pathway. The constraints and restraints are essential components of the computational protocol. 

Fig. 20. Schematic representation of the reaction coordinate for tryptophan fluorescence quenching induced by hydrogen transfer and aborted decarboxylation. The electronic nature of the Si surface changes character along the Si path due to two avoided crossings between jSi and S2 The first one occurs between the covalent state and the ionic La state along the reaction coordinate that interconverts the i9i-Min and. Si-Exc minima. The second one occurs between the ionic La state and the biradical Bi, state along the tautomerization coordinate that leads to the excited-state tautomerized form S -Taut. This point does not corresponds to a minimum on the potential-energy surface and it is found that evolution along a decarboxylation coordinate leads to a -Si /-So conical intersection, where efficient radiationless decay to the ground state takes place. The values of the relevant structural parameters are given in A. Data from Ref. 102.

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