Note

This website is presently under development. The primary website for MOPAC is still http://openmopac.net until the majority of its contents have been migrated here.

NOOPT

Turn off all optimization flags for atoms of type X.  This keyword is useful for partial geometry optimizations.  If “-X’” is missing, turn off all optimization flags. If OPT-X  is present, optimization flags can be turned on after NOOPT has been run, so to optimize the positions of hydrogen atoms while freezing the positions of all other atoms, use “NOOPT OPT-H”.

If  OPT("label"=n.nn)is present, then this will be run first, then NOOPT will turn off all optimization flags for atoms containing the label “label”.