Obviously a level of theory, basis set, and starting molecular geometry must be specified to begin a geometry optimization or transition-structure search. These aspects are described elsewhere in this manual, and this section describes job-control variables specific to optimizations.
$molecule 0 1 O H 1 oh H 1 oh 2 hoh oh = 1.1 hoh = 104 $end $rem JOBTYPE freq Calculate an analytic Hessian METHOD hf BASIS 6-31g(d) $end $comment Now proceed with the optimization making sure to read in the analytic Hessian (use other available information too). $end @@@ $molecule read $end $rem JOBTYPE opt METHOD hf BASIS 6-31g(d) SCF_GUESS read GEOM_OPT_HESSIAN read Have the initial Hessian $end
$molecule 0 1 O H 1 r H 1 r 2 ang r 0.95 ang 104.5 $end $rem JOBTYPE OPT METHOD HF BASIS STO-3G GEOM_OPT_COORDS 2 $end