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METHOD = optimization selection switch. You can choose STANDARD or SCHLEGEL (the default is STANDARD).
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)
DXMAX = initial trust radius of the step, in Bohr. Steps will be scaled down to this value, if necessary. (default=0.2, except STANDARD method geometry searches, when it is 0.3) the next three apply only to METHOD=STANDARD
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)
TRMIN = minimum permissible value of the trust radius. (default=0.01)
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) = 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)
IFREEZ = array of internal coordinates to freeze. For example, IFREEZ(1)=1,3 would freeze the two bond lengths in the $ZMAT example, while optimizing the angle. You cannot freeze coordinates using Cartesian coordinates.
IFOLOW = Mode selection switch, for RUNTYP=SADPOINT. For METHOD=STANDARD, 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. (default is 1) 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 Punch occ orbitals after 0, and HESS at all 0 Punch occ orbitals after 0, but all orbitals at geometry 0 (default) -1 Punch occ orbitals at 0+L only -2 Never punch orbitals
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.)
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.)
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 STANDARD POWELL default for SADPOINT using STANDARD SCHLEGEL only choice for METHOD=SCHLEGEL
RESTAR = Enables restart of an optimization run. This can only be used with IREST .ne. 0 in $CONTRL. Use of this variable is discouraged. ---- 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 colinear. (default=0.07)
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