Automatic geometry optimization is invoked using the OPTG command. The OPT command available in previous MOLPRO versions is no longer needed and not available any more.
OPTG[, key1=value, key2=value,......]
The OPTG command can be used to perform automatic geometry optimizations for all kinds of wavefunctions. For minimum searches, it is usually sufficient to give just the OPTG command without further options or directives, but many options are available which are described in the following sections.
Various optimization methods can be selected as described in section 39.2.1. MOLPRO allows minimization (i.e. search for equilibrium geometries), transition state optimization (i.e. search for saddle points on energy surfaces), and reaction path following. The standard algorithms are based on the rational function approach and the geometry DIIS approach. Also available is the quadratic steepest descent following method of Sun and Ruedenberg (see J. Sun and K. Ruedenberg, J. Chem. Phys. 99, 5257 (1993)). This method is often advantageous in Transition State searches. For a detailed discussion of the various minimization algorithms see F. Eckert, P. Pulay and H.-J. Werner, J. Comp. Chem 18, 1473 (1997). Reaction path following is described in F. Eckert and H.-J. Werner, Theor. Chem. Acc. 100, 21, (1998). Please refer to the references section for citations of the analytic gradient methods.
When analytical gradients are available for the optimized energy these will be used. Otherwise the gradient will be computed numerically from finite energy differences. Normally, the last computed ground-state energy is used. But the VARIABLE directive or option can be used to optimize, e.g., Davidson corrected energies, excited states, or counterpoise corrected energies.
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