The geometry optimization termination criteria (see Criteria) in both gradient minimization and energy minimization can be over-ridden by specifying a gradient norm requirement. For example, GNORM=20 would allow the geometry optimization to exit as soon as the gradient norm dropped below 20.0, the default being 1.0.
For high-precision work, GNORM=0.0 is recommended. Unless LET is also used, the GNORM will be set to the larger of 0.01 and the specified GNORM. Results from GNORM=0.01 are easily good enough for all high-precision work.
N.b.: Do not confuse GNORM, the keyword, with GNORM, the value of the scalar of the calculated gradient.