W.Quapp

Chemical Physics Letters 253 (1996) 286-292 

"A gradient-only algorithm for tracing a reaction path uphill to the saddle
of a potential energy surface" 


We propose a procedure to follow weakest ascent along a valley using
gradient-only calculations. The device allows one to search for saddles 
starting somewhere near a minimum provided that the saddle is connected
with the minimum by a valley. 
We define a local criterion for a minimum energy
path by comparison of gradients. The algorithm is a predictor-corrector
method using two parameters: step length and tolerance. There is no 
need for a guess of the saddle point region.
We calculate valley pathways on 2D test examples, on the HCN surface,
and on a 12D potential of an argon 4-cluster.