Saddle point geometry reaction paths

The first basis set was employed in most of the calculations, and, particularly, in the determination of the saddle point geometry and the minimun energy path (see Sec.4). The second basis set was used mainly to improve the calculated barrier height and the exoergicity of the reaction (see Sec.5). 

Newton search to reproduce fee WD saddle point geometry, barrier height, and imaginary frequency as closely as possible. Specifically, a Newton search for simultaneous zeros for the relative errors in V, , a, 0, and R weighted by factors of 50, 50, 10, 1, and 10, respectively, was run for several (typically 10) iterations. (3) For each choice of the five constants in (2), the values of fee five constants Cj, tj, g, f , and z were determined by a converged Newton search so feat fee WD frequencies for the five bound vibrational modes at fee saddle point are reproduced. (4) As a final independent step, the values of the five constants fp, Pp, Rp, h, and R were chosen as a group by trial and error to ensure that the a" frequency behaves as reasonably as possible along the reaction path. (The value of z was then readjusted to yield the WD value for fee a" frequency at the saddle point.)... 

An IRC calculation examines the reaction path leading down from a transition structure on a potential energy surface. Such a calculation starts at the saddle point and follows the path in both directions from the transition state, optimizing the geometry of the molecular system at each point along the path. In this way, an IRC calculation definitively connects two minima on the potential energy surface by a path which passes through the transition state between them. 

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