By default, geometry optimization is terminated when the gradient norm drops below the pre-set MOPAC criterion or the value defined in the MOPAC reference data file, if keyword GNORM is present. If the PARAM keyword GNORM=n.n is present, the effect is to add the MOPAC keyword GNORM=n.n to most MOPAC data files. If a MOPAC data file already contains the keyword GNORM, then that data set will not be modified. The PARAM keyword GNORM=n.n is useful in reducing the geometry optimization criterion when high precision is not needed. It saves a lot of CPU time.