Specifies the eigenvector of the hessian to be followed.

*root*=1- specifies a minimization (default).
*root*=2- specifies a transition state (saddle point) optimization.

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 46.2.7) or using a precomputed hessian (see section 46.2.6).

molpro@molpro.net 2018-03-18