where *key* can be

`IDIR`- If starting at a transition state (or near a transition state)
determine where to take the first step. If
`IDIR=0`is chosen, the first step will be towards the transition state. This is the default. If`IDIR=1`is given in the input the first optimization step will be along the ”transition vector” i.e. the hessian eigenvector to the smallest eigenvalue which points down towards the minimum. If using a larger`IDIR`parameter, the first step will be larger; if using a negative value, the first step will be in the opposite direction. `STPTOL`- If using an updated hessian matrix, this parameter determines what
update to take. If the step size between two subsequent points on which the steepest decent
lines are puzzled together is smaller than
*stptol*(i.e. if we are close to a minimum) the BFGS update is used, otherwise it is Powell update. The default value of*stptol*is . Note that the stepsize is also affected by the`STEPMAX`option. `SLMAX`- This option is only valid with the old version
of the reaction path following algorithm (i.e.
`METHOD,SRSTEEP`). In this algorithm`slmax`determines the frequency of the recalculation of the numerical hessian. If the total step size of the last steps exceeds*slmax*the hessian will be recalculated, otherwise it will be updated. By default*slmax*is two times the maximum step size of the optimization step*steplength*(see`STEP`section 46.2.12). If you are using`METHOD,QSD`, the`SLMAX`option is obsolete and the`NUMHES`command (see above) should be used instead.

These options can also be given on the `OPTG` command line.

molpro@molpro.net 2019-03-22