With the block key GEOMETRY you define the runtype and strategy parameters.
GEOMETRY
{RunType RunTypeData}
{Optim Cartesian|Delocal}
{Iterations Niter}
{Converge {E=TolE} {Grad=TolG} {Rad=TolR}}
{Step {TrustRadius=MaxRadius}}
End
RunType
RunTypeData
Can be:
- SinglePoint or SP
- GeometryOptimization or GO
- TransitionState or TS
- Frequencies or F
If omitted the run type is GeometryOptimization.
If the key GEOMETRY
is not used at all the run type is SinglePoint.
Optim
Cartesian|Delocal
Optimization in delocalized coordinates (Delocal) can only be used in geometry optimizations or transition state searches.
Iterations
Niter
The maximum number of geometry iterations allowed to locate the desired
structure. The default is 50.
This is a fairly large number. If the geometry has not converged (at least to a
reasonable extent) within that many iterations you should sit down and
consider the underlying cause rather than simply increase the allowed number of
cycles and try again.
Converge
Convergence is monitored for two items: the energy and the Cartesian gradients. Convergence criteria can be specified separately for each of these items:
TolE
The criterion for changes in the energy, in Hartrees. Default: 1e-5.
TolG
Applies to gradients, in Hartree/angstrom. Default: 1e-3.
TolR
The maximum Cartesian step allowed for a converged geometry. Default: 0.001 Angstrom.
Step
Controls that changes in geometry from one cycle to another are not too large:
MaxRadius
By default, the trust radius is set to 0.2. Using the key, the user can override this, setting a constant value. A conservative value is 0.2. A large system (eg 100 atoms) typically needs a larger trust radius (eg 0.8).
