LET — Do not reduce gradients in FORCE.

LET

In cases where the force constant matrix is computed by invocation of
FORCE, AMPAC will
calculate the gradients of the input geometry and halt execution if the gradient norm is not
less than 3.0 to ensure that the computation is carried out on a fully minimized geometry. The
LET keyword allows the calculation to be completed without regard to this test. It should be
emphasized that force constants at any place other than a fully optimized stationary point are
*undefined*. LET should be used with extreme care. See
Chapter 4, *Computational Procedures* for a
discussion of stationary point
characterization.

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