MOLPRO

42 GEOMETRY OPTIMIZATION (OPTG) 310
QSD
SRMIN
type may be GRAD interpolation using the gradients (default), working
good for rigid molecules, STEP interpolation using Quasi-Newton
steps which could be advantageous in dealing with very floppy molecules,
ENER interpolation using energies, which is an intermediate between
the above two.
Quadratic steepest descent method of Sun and Ruedenberg.
Old version of QSD.
For transition state searches (invoked with the ROOT option, see section 42.2.11) key can be
RF
DIIS
QSD
SRTRANS
Rational Function method (default).
Pulay’s Geometry DIIS method (see above).
Quadratic Steepest Descent Transition State search using the image
Hessian method (see J. Sun and K. Ruedenberg, J. Chem. Phys. 101,
2157 (1994)) The use of this option is recommended for transition
state searches – especially in complicated cases. The optimization
step is checked and the Hessian is recalculated when approaching a
troublesome region of the PES. Thus this method is somewhat safer
(and often faster) in reaching convergence than the RF or DIIS
method. The Hessian recalculation safeguard may be turned off using
the METHOD,QSD,NOHESS input card.
Old version of QSD.
For reaction path following the input key is
QSDPATH
SRSTEEP
Quadratic Steepest Descent reaction path following. This methods
determines reaction paths (intrinsic reaction coordinates, IRCs) by
following the exact steepest descent lines of subsequent quadratic approximations
to the potential energy surface. The Hessian matrix is
calculated numerically at the first optimization step and subsequently
updated by Powell or BFGS update. If a given arc length of the steepest
descent lines is exceeded, the Hessian is recalculated numerically
(see OPTION section 42.2.16). For details see J. Sun and K. Ruedenberg,
J. Chem. Phys. 99, 5269 (1993) It is also possible to recalculate
the Hessian after each m steps using the NUMHES,m command (see
section 42.2.7). If the Hessian matrix is recalculated in every optimization
step (NUMHES,1) a algorithm different to the one with updated
Hessians is used, which is very accurate. Using the PRINT,OPT
card, this algorithm prints in every optimization step a reaction path
point r which is different from the point where the energy and the
gradient is calculated but closer to the real reaction path (for further
details of the algorithm see J. Sun and K. Ruedenberg, J. Chem. Phys.
99, 5257 (1993)). For further input options of the QSD reaction path
following see OPTION section 42.2.16.
Old Version of QSDPATH.
42.2.2 Optimization coordinates (COORD)
It is possible to use various coordinate types and algorithms for the optimization. This can be
controlled by additional subcommands as described in this and the following subsections.