CASTEP > Dialogs in CASTEP > CASTEP Calculation dialog > Setup tab > CASTEP Elastic Constants dialog > Options tab

Options tab

The Options tab allows you to specify the convergence level of the elastic constants calculation.

Quality: Sets the convergence thresholds for energy change, maximum force, and maximum displacement between cycles. This is used for the geometry optimization runs that are required for the elastic constants calculation. The calculation will stop when all of these criteria are satisfied.

Four sets of convergence thresholds are available; Coarse, Medium, Fine and Ultra-fine. The values of each convergence threshold in each set are given in the table below:

Quality Energy (eV/atom) Force (eV/Å) Displacement (Å)
Coarse 1 × 10-5 0.02 0.001
Medium 4 × 10-6 0.01 4 × 10-4
Fine 2 × 10-6 0.006 2 × 10-4
Ultra-fine 1 × 10-6 0.002 1 × 10-4
Customized User defined User defined User defined

Alternatively, thresholds can be specified independently. If user defined values are used, the Quality displayed is Customized.

When the main quality is set to Express the elastic constants quality is also set to Express. In this case energy tolerance will be displayed in eV/cell rather than eV/atom, the default value is 0.001 eV/cell. All other tolerances are ignored and geometry optimization runs stop when the energy change is less than the tolerance regardless of the values of forces or displacements.

Energy: Specify the convergence threshold for the maximum energy change, in eV/atom. The units are eV/cell if the Quality is set to Express.

Max. force: Specify the convergence threshold for the maximum force, in eV/Å. If the Quality is set to Express, this tolerance by default will be set to a very high value and will effectively be ignored in the calculation.

Max. displacement: Specify the convergence threshold for the maximum displacement, in Å. If the Quality is set to Express, this tolerance by default will be set to a very high value and will effectively be ignored in the calculation.

Max. iterations: Specify the maximum number of elastic constants cycles. If this number of cycles is reached, then the calculation will stop even if the convergence criteria are not satisfied.

Access methods

Menu Modules | CASTEP | Calculation | Setup | More... | Options
Toolbar | Calculation | Setup | More... | Options
See Also:

Elastic constants theory
CASTEP Elastic Constants task
CASTEP Elastic Constants dialog
Elastic Constants tab - CASTEP Elastic Constants dialog

Accelrys Materials Studio 8.0 Help: Wednesday, December 17, 2014
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