GANNEAL — Simulated annealing search for extrema within an energy range.
The GANNEAL method locates a set of stationary points on a potential energy surface by a procedure employing a mixture of non-local simulated annealing and gradient minimization.
GANNEAL differs from ANNEAL in that it searches only within a specified energy range (the “crenel”) and uses gradient minimizations rather than energy minimizations. This allows location of transition states as well as minima.
GANNEAL differs from TSANNEAL and ANNEAL in that the RMS gradient norm (gnorm) is used in place of energy in the Metropolis step. Using gnorm focuses the simulated annealing search on all critical points rather than primarily on just minima.
See Chapter 13, Simulated Annealing for discussion of the use of this method as well as an explanation of the dedicated keywords used in the annealing procedure. By default, TRUSTG is used in the quenching phase but TS can be used to override this default. LTRD may also be specified for a subsequent quenching phase using a full Hessian.
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