MOLPRO

42 GEOMETRY OPTIMIZATION (OPTG) 304
ACTIVE,variables
If this card is present, all variables which are not specified are inactive. Alternatively,
INACTIVE,variables
In this case all variables that are not given are active.
41.3 Saving the gradient in a variables
If the directive
VARSAV
is given, the gradient is saved in variables GRADX, GRADY, GRADZ. GRADX(n) is the derivative
with respect to x for the n-th atom. The atoms are in the order as printed. This order can be
different from the order in the input z-matrix, since the centres are reordered so that all atoms
of the same type follow each other.
42 GEOMETRY OPTIMIZATION (OPTG)
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 42.2.1. 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.
By default the program repeats in each geometry optimization step those commands in the input
that are needed to compute the last energy. For example, for MP2 gradients the commands HF
and MP2 are needed. The MP2 gradients will then be computed automatically. It is also possible
to define procedures for the energy calculation, or to specify the first command from which the
input should be repeated in each step (see section 42.1.1). The section of the input which is
needed for the geometry optimization must not modify variables that are used in the geometry
definition (changes of such variables are ignored, and a warning message is printed).