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".