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# 9.1.2 Job Control

(February 4, 2022)

Obviously a level of theory, basis set, and starting molecular geometry must be specified to begin a geometry optimization or transition-structure search. These aspects are described elsewhere in this manual, and this section describes job-control variables specific to optimizations.

JOBTYPE

JOBTYPE
Specifies the calculation.
TYPE:
STRING
DEFAULT:
Default is single-point, which should be changed to one of the following options.
OPTIONS:
OPT Equilibrium structure optimization. TS Transition structure optimization. RPATH Intrinsic reaction path following.
RECOMMENDATION:
Application-dependent.

GEOM_OPT_HESSIAN

GEOM_OPT_HESSIAN
Determines the initial Hessian status.
TYPE:
STRING
DEFAULT:
DIAGONAL
OPTIONS:
DIAGONAL Set up diagonal Hessian. READ Have exact or initial Hessian. Use as is if Cartesian, or transform if internals.
RECOMMENDATION:
An accurate initial Hessian will improve the performance of the optimizer, but is expensive to compute.

GEOM_OPT_COORDS

GEOM_OPT_COORDS
Controls the type of optimization coordinates.
TYPE:
INTEGER
DEFAULT:
$-$1
OPTIONS:
0 Optimize in Cartesian coordinates.  1 Generate and optimize in internal coordinates, if this fails abort. $-$1 Generate and optimize in internal coordinates, if this fails at any stage of the optimization, switch to Cartesian and continue.  2 Optimize in $Z$-matrix coordinates, if this fails abort. $-$2 Optimize in $Z$-matrix coordinates, if this fails during any stage of the optimization switch to Cartesians and continue.
RECOMMENDATION:
Use the default, as delocalized internals are more efficient. Note that optimization in $Z$-matrix coordinates requires that the input be specified in $Z$-matrix format.

TYPE:
INTEGER
DEFAULT:
300 $\equiv 300\times 10^{-6}$ tolerance on maximum gradient component.
OPTIONS:
$n$ Integer value (tolerance = $n\times 10^{-6}$).
RECOMMENDATION:
Use the default. To converge GEOM_OPT_TOL_GRADIENT and one of GEOM_OPT_TOL_DISPLACEMENT and GEOM_OPT_TOL_ENERGY must be satisfied.

GEOM_OPT_TOL_DISPLACEMENT

GEOM_OPT_TOL_DISPLACEMENT
Convergence on maximum atomic displacement.
TYPE:
INTEGER
DEFAULT:
1200 $\equiv 1200\times 10^{-6}$ tolerance on maximum atomic displacement.
OPTIONS:
$n$ Integer value (tolerance = $n\times 10^{-6}$).
RECOMMENDATION:
Use the default. To converge GEOM_OPT_TOL_GRADIENT and one of GEOM_OPT_TOL_DISPLACEMENT and GEOM_OPT_TOL_ENERGY must be satisfied.

GEOM_OPT_TOL_ENERGY

GEOM_OPT_TOL_ENERGY
Convergence on energy change of successive optimization cycles.
TYPE:
INTEGER
DEFAULT:
100 $\equiv 100\times 10^{-8}$ tolerance on maximum (absolute) energy change.
OPTIONS:
$n$ Integer value (tolerance = value $n\times 10^{-8}$).
RECOMMENDATION:
Use the default. To converge GEOM_OPT_TOL_GRADIENT and one of GEOM_OPT_TOL_DISPLACEMENT and GEOM_OPT_TOL_ENERGY must be satisfied.

GEOM_OPT_MAX_CYCLES

GEOM_OPT_MAX_CYCLES
Maximum number of optimization cycles.
TYPE:
INTEGER
DEFAULT:
50
OPTIONS:
$n$ User defined positive integer.
RECOMMENDATION:
The default should be sufficient for most cases. Increase if the initial guess geometry is poor, or for systems with shallow potential wells.

GEOM_OPT_PRINT

GEOM_OPT_PRINT
Controls the amount of Optimize print output.
TYPE:
INTEGER
DEFAULT:
3 Error messages, summary, warning, standard information and gradient print out.
OPTIONS:
0 Error messages only. 1 Level 0 plus summary and warning print out. 2 Level 1 plus standard information. 3 Level 2 plus gradient print out. 4 Level 3 plus Hessian print out. 5 Level 4 plus iterative print out. 6 Level 5 plus internal generation print out. 7 Debug print out.
RECOMMENDATION:
Use the default.

GEOM_OPT_SYMFLAG

GEOM_OPT_SYMFLAG
Controls the use of symmetry in Optimize.
TYPE:
LOGICAL
DEFAULT:
TRUE
OPTIONS:
TRUE Make use of point group symmetry. FALSE Do not make use of point group symmetry.
RECOMMENDATION:
Use the default.

GEOM_OPT_MODE

GEOM_OPT_MODE
Determines Hessian mode followed during a transition state search.
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
0 Mode following off. $n$ Maximize along mode $n$.
RECOMMENDATION:
Use the default, for geometry optimizations.

GEOM_OPT_MAX_DIIS

GEOM_OPT_MAX_DIIS
Controls maximum size of subspace for GDIIS.
TYPE:
INTEGER
DEFAULT:
0
OPTIONS:
0 Do not use GDIIS. -1 Default size = min(NDEG, NATOMS, 4) NDEG = number of molecular degrees of freedom. $n$ Size specified by user.
RECOMMENDATION:
Use the default or do not set $n$ too large.

GEOM_OPT_DMAX

GEOM_OPT_DMAX
Maximum allowed step size. Value supplied is multiplied by 10${}^{-3}$.
TYPE:
INTEGER
DEFAULT:
300 = 0.3
OPTIONS:
$n$ User-defined cutoff.
RECOMMENDATION:
Use the default.

GEOM_OPT_UPDATE

GEOM_OPT_UPDATE
Controls the Hessian update algorithm.
TYPE:
INTEGER
DEFAULT:
-1
OPTIONS:
-1 Use the default update algorithm.  0 Do not update the Hessian (not recommended).  1 Murtagh-Sargent update.  2 Powell update.  3 Powell/Murtagh-Sargent update (TS default).  4 BFGS update (OPT default).  5 BFGS with safeguards to ensure retention of positive definiteness (GDIIS default).
RECOMMENDATION:
Use the default.

GEOM_OPT_LINEAR_ANGLE

GEOM_OPT_LINEAR_ANGLE
Threshold for near linear bond angles (degrees).
TYPE:
INTEGER
DEFAULT:
165 degrees.
OPTIONS:
$n$ User-defined level.
RECOMMENDATION:
Use the default.

FDIFF_STEPSIZE

FDIFF_STEPSIZE
Displacement used for calculating derivatives by finite difference.
TYPE:
INTEGER
DEFAULT:
100 Corresponding to 0.001 Å. For calculating second derivatives.
OPTIONS:
$n$ Use a step size of $n\times 10^{-5}$.
RECOMMENDATION:
Use the default except in cases where the potential surface is very flat, in which case a larger value should be used. See FDIFF_STEPSIZE_QFF for third and fourth derivatives.

Example 9.1  As outlined, the rate of convergence of the iterative optimization process is dependent on a number of factors, one of which is the use of an initial analytic Hessian. This is easily achieved by instructing Q-Chem to calculate an analytic Hessian and proceed then to determine the required critical point

$molecule 0 1 O H 1 oh H 1 oh 2 hoh oh = 1.1 hoh = 104$end

$rem JOBTYPE freq Calculate an analytic Hessian METHOD hf BASIS 6-31g(d)$end

$comment Now proceed with the optimization making sure to read in the analytic Hessian (use other available information too).$end

@@@

$molecule read$end

$rem JOBTYPE opt METHOD hf BASIS 6-31g(d) SCF_GUESS read GEOM_OPT_HESSIAN read Have the initial Hessian$end


View output

Example 9.2  Optimization in $Z$-matrix coordinates. The input must be specified in $Z$-matrix format with coordinates specified. In the example below there are two coordinates representing the bond length and bond angle of a water molecule.

$molecule 0 1 O H 1 r H 1 r 2 ang r 0.95 ang 104.5$end

$rem JOBTYPE OPT METHOD HF BASIS STO-3G GEOM_OPT_COORDS 2$end


View output