Specifies the eigenvector of the hessian to be followed.
In the present implementation a saddle point search is possible with the rational function method (METHOD,RF), the geometry DIIS method (METHOD,DIIS) and the quadratic steepest descent method of Sun and Ruedenberg (METHOD,SRTRANS).
Note that convergence is usually much more difficult to achieve than for minimizations. In particular, a good starting geometry and a good approximation to the hessian is needed. The latter is achieved by evaluating the hessian numerically (see section 39.2.7) or using a precomputed hessian (see section 39.2.6).