Intrinsic Reaction Coordinate (IRC)
For insight in the properties of a full reaction path the LT functionality provides only very crude information. An alternative and more advanced procedure to trace the path of a chemical reaction is provided by the intrinsic reaction coordinate (IRC) method as implemented in ADF. The basic idea is to start at a transition state and slide down the hill towards the adjacent local minimum, at either side of the transition state, by following the line of steepest decent in the metric of mass-weighted coordinates. A full determination of the path does not only produce the height of the barrier in a reaction, but also provides information for thermodynamic properties, the reaction rate and dynamics; the details of such analysis have not yet been implemented in ADF.
The calculation starts by taking steps of controlled length (in the mass-weighted metric) towards the minimum by determining the minimum on the local sphere around a given point along the path, with as radius the chosen step length. The calculation, therefore, consists, as in the linear transit method, of a sequence of constrained optimizations, and terminates when the adjacent minima to the TS have been identified.
Links
ADF User Documentation: IRC
ADF-GUI: structure and reactivity,
Tutorial:
reactivity
Examples: reactivity
References: IRC
Related: transition states, linear transit
The SN2 substitution at carbon and silicon. With ADF one can understand why it proceeds via qualitatively different potential energy surfaces.
