Interpolate the geometry of the stationary point (minimum or saddle
point) by a quartic polynomial between the current and the previous
geometry. If *iflag*=0 or no *iflag* is set, the next
optimization step will be taken from the interpolated geometry using
the interpolated energy and gradient. If *iflag*=1 the energy
and gradient will be recalculated at the interpolated geometry
before taking the new optimization step. Note though, that the
additional effort of recalculating the energy and gradient is usually
not met by the increase of the convergence rate of the optimization.
*thrlmin* and *thrlmax* are min and max thresholds for the
recalculation of the energy and the gradient in case *iflag*=1.
I.e. the recalculation just takes place if the interpolated geometry
isn't too close to the actual geometry *thrlmin* and isn't too
remote from the actual geometry *thrlmax*.
Default values are *thrlmin*=0.001 and *thrlmax*=0.05 in the
scaled parameter space of the optimization.

molpro@molpro.net 2018-09-24