| Startseite |
This group controls the search for stationary points. Note that NZVAR in
$CONTRL determines if the geometry search is conducted in Cartesian or internal
coordinates.
METHOD = optimization algorithm selection. Pick from
NR Straight Newton-Raphson iterate. This will attempt to
locate the nearest stationary point, which may be of any
order. There is no steplength control. RUNTYP can be
either OPTIMIZE or SADPOINT
RFO Rational Function Optimization. This is one of the
augmented Hessian techniques where the shift
parameter(s) is(are) chosen by a rational function
approximation to the PES. For SADPOINT searches it
involves two shift parameters. If the calculated stepsize is
larger than DXMAX the step is simply scaled down to size.
QA Quadratic Approximation. This is another version of an
augmented Hessian technique where the shift parameter is
chosen such that the steplength is equal to DXMAX. It is
completely equivalent to the TRIM method. (default)
SCHLEGEL The quasi-NR optimizer by Schlegel.
CONOPT CONstrained OPTimization. An algorithm which can be used
for locating TSs. The starting geometry MUST be a
minimum! The algorithm tries to push the geometry uphill
along a chosen Hessian mode (IFOLOW) by a series of
optimizations on hyperspheres of increasingly larger
radii. Note that there currently are no restart capabilitites
for this method, not even manually.
OPTTOL = gradient convergence tolerance, in Hartree/Bohr. Convergence of a
geometry search requires the largest component of the gradient to be less
than OPTTOL, and the root mean square gradient less than 1/3 of OPTTOL.
(default=0.0001)
NSTEP =
maximum
number of
steps to
take. Restart
data
is
punched
if
NSTEP
is
exceeded. (default=20)
• the next four control the step size
DXMAX = initial trust radius of the step, in Bohr.
For METHOD=RFO, QA, or SCHLEGEL, steps will be scaled down to this
value, if necessary. (default=0.3 for OPTIMIZE and 0.2 for SADPOINT)
For METHOD=NR, DXMAX is inoperative.
For METHOD=CONOPT, DXMAX is the step along the previous two points to
increment the hypersphere radius between constrained optimizations.
(default=0.1)
• the next three apply only to METHOD=RFO or QA:
TRUPD = a flag to allow the trust radius to change as the geometry search
proceeds.
(default=.TRUE.)
TRMAX = maximum permissible value of the trust radius.
(default=0.5 for OPTIMIZE and 0.3 for SADPOINT)
TRMIN = minimum permissible value of the trust radius. (default=0.05)
• the next three control mode following
IFOLOW = Mode selection switch, for RUNTYP=SADPOINT.
For METHOD=RFO or QA, the mode along which the energy is maximized,
other modes are minimized. Usually refered to as "eigenvector following".
For METHOD=SCHLEGEL, the mode whose eigenvalue is (or will be made)
negative. All other curvatures will be made positive.
For METHOD=CONOPT, the mode along which the geometry is initially
perturbed from the minima. (default is 1)
In Cartesian coordinates, this variable doesn't count the six translation
and rotation degrees. Note that the "modes" aren't from mass-weighting.
STPT = flag to indicate whether the initial geometry is considered a stationary
point. If .true. the initial geometry will be perturbed by a step along the
IFOLOW normal mode with stepsize STSTEP. (default=.false.) The positive
direction is taken as the one where the largest component of the Hessian
mode is positive. If there are more than one largest component
(symmetry), the first is taken as positive.
Note that STPT=.TRUE. has little meaning with HESS=GUESS as there will
be many degenerate eigenvalues.
STSTEP = Stepsize for jumping off a stationary point. Using values of 0.05 or
more
may work better. (default=0.01)
IFREEZ = array of coordinates to freeze. These may be internal or Cartesian
coordinates. For example, IFREEZ(1)=1,3 freezes the two bond lengths
in the $ZMAT example, while optimizing the angle. If NZVAR=0, so that
this value applies to the Cartesian coordinates instead, the input of
IFREEZ(1)=4,7 means to freeze the x coordinates if the 2nd and 3rd
atoms in the molecule.
See also IFZMAT and FVALUE in $ZMAT, and IFCART below, as IFREEZ does
not apply to DLC internals.
In a numerical Hessian run, IFREEZ specifies Cartesian displacements to
be skipped for a Partial Hessian Analysis. For more information: J.D.
Head, Int. J. Quantum Chem. 65, 827, 1997 H. Li, J.H. Jensen,
manuscript in preparation.
IFCART = array of Cartesian coordinates to freeze during a geometry optimization
using delocalized internal coordinates.
• The next two control the hessian matrix quality
HESS = selects the initial hessian matrix.
= GUESS chooses a positive definite diagonal hessian. (default for
RUNTYP=OPTIMIZE)
= READ causes the hessian to be read from a $HESS group. (default
for RUNTYP=SADPOINT)
= RDAB reads only the ab initio part of the hessian, and
approximates the effective fragment blocks.
= RDALL reads the full hessian, then converts any fragment blocks
to 6x6 T+R shape. (this option is seldom used).
= CALC causes the hessian to be computed, see the $FORCE group.
IHREP = the number of steps before the hessian is recomputed. If given as 0, the
hessian will be computed only at the initial geometry if you choose
HESS=CALC, and never again. If nonzero, the hessian is recalculated
every IHREP steps, with the update formula used on other steps.
(default=0)
• the next two control the amount of output
Let 0 mean the initial geometry, L mean the last geometry, and all mean
every geometry. Let INTR mean the internuclear distance matrix. Let HESS
mean the approximation to the hessian. Note that a directly calculated hessian
matrix will always be punched, NPUN refers only to the updated hessians
used by the quasi-Newton step.
NPRT = 1 Print INTR at all, orbitals at all
0 Print INTR at all, orbitals at 0+L (default)
-1 Print INTR at all, orbitals never
-2 Print INTR at 0+L, orbitals never
NPUN = 3 Punch all orbitals and HESS at all
2 Punch all orbitals at all
1 same as 0, plus punch HESS at all
0 Punch all orbitals at 0+L, otherwise only occupied
orbitals (default)
-1 Punch occ orbitals at 0+L only
-2 Never punch orbitals
HSSEND = a flag to control automatic hessian evaluation at the end of a
successful
geometry search. (default=.FALSE.)
---- the following parameters are quite specialized ----
PURIFY = a flag to help eliminate the rotational and translational degrees of
freedom
from the initial hessian (and possibly initial gradient). This is much like
the variable of the same name in $FORCE, and will be relevant only if
internal coordinates are in use. (default=.FALSE.)
$STATPT, $TRUDGE
PROJCT = a flag to eliminate translation and rotational degrees of freedom from
Cartesian optimizations. The default is .TRUE. since this normally will
reduce the number of steps, except that this variable is set false when
POSITION=FIXED is used during EFP runs.
ITBMAT = number of micro-iterations used to compute the step in Cartesians which
corresponds to the desired step in internals. The default is 5.
UPHESS = SKIP do not update Hessian (not recommended)
BFGS default for OPTIMIZE using RFO or QA
POWELL default for OPTIMIZE using NR or CONOPT
POWELL default for SADPOINT
MSP mixed Murtagh-Sargent/Powell update
SCHLEGEL only choice for METHOD=SCHLEGEL
MOVIE = a flag to create a series of structural data which can be show as a
movie by
the Macintosh program Chem3D. The data is written to the file IRCDATA.
(default=.FALSE.)
---- NNEG, RMIN, RMAX, RLIM apply only to SCHLEGEL ----
NNEG = The number of negative eigenvalues the force constant matrix should have.
If necessary the smallest eigenvalues will be reversed. The default is 0
for RUNTYP=OPTIMIZE, and 1 for RUNTYP=SADPOINT.
RMIN = Minimum distance threshold. Points whose root mean square distance
from the current point is less than RMIN are discarded.
(default=0.0015)
RMAX = Maximum distance threshold. Points whose root mean square distance
from the current point is greater than RMAX are discarded. (default=0.1)
RLIM = Linear dependence threshold. Vectors from the current point to the
previous points must not be collinear. (default=0.07)
• See the 'further information' section for some help
with OPTIMIZE and SADPOINT runs