Convergence Tools: Brillouin Zone sampling

In this type of project, ASAP will run a set of single-point calculations using the selected Brillouin zone (BZ) sampling grids. ASAP uses Monkhorst-Pack grids to sample the Brillouin zone. A Monkhorst-Pack grid is a set of evenly spaced k-points and is specified by 3 numbers: the number of points along each axis in reciprocal space.

The project starts with the definition of the atomic structure. We refer the user to section Structure Modeling in ASAP for further information on ASAP structure builder/viewer interface.

After the atomic structure is defined, edit the type of project,

from the list of possible project types implemented in ASAP, select Convergence tools: BZ sampling.

Then click on the Parameters icon to open the Convergence tools: BZ sampling parameters widget.

On the right side of the Parameter widget, you can see the Monkhorst-Pack grid that will be used for each of the single-point calculations. You can modify the BZ sampling by tuning the following parameters:

• Monkhorst-Pack grid. Initial Monkhorst-Pack grid.

  ASAP also indicates the corresponding k-grid cutoff, a parameter determining the fineness of the k-grid used for Brillouin zone sampling. The k-grid cutoff is half the length of the smallest lattice vector of the supercell required to obtain the same sampling precision with a single k point.

• Scaling of Monkhorst-Pack grid. The minimum (initial) and maximum (final) scaling applied to the MP grid previously indicated.

• Number of grids. To indicate the total number of grids to be created.

• Type of grids. To indicate if you desire to include only even or odd Monkhorst-Pack grids.

  

Press the Update BZ samplings button to update the list of grids displayed in the right side of the Parameter widget.

Press the OK button to close the IET widget once the parameters are properly set.

Click on the Calculator icon to select the computational engine to be used during geometry optimisation.

The Convergence Tool: BZ sampling is only compatible with the SIESTA calculator. We refer the user to chapter The SIESTA Calculator for further information on SIESTA calculator.

Click on the Run icon to open the Run widget. Then click on the Run button to submit the set of calculations required to perform the BZ sampling.

We refer the user to chapter Runners for further information on computational resources configuration in ASAP.

After submitting a job (run), the Calculator output tab in the Run widget shows the complete calculation output in real time.

In addition, the Task output tab in the Run widget shows relevant information of Geometry optimisation output in real-time.

Convergence Tools. Brillouin Zone sampling workflow: Analysis

When the calculation is completed, select Exit and analyse to open the analysis widget.

Select one of the Plot type options to visualise the energy deviation, maximal force deviation or Frobenius norm of stress deviation computed for each of the used Brillouin zone (BZ) sampling grids. Each deviation is computed using the corresponding value obtained with the highest BZ sampling grid.