Calculate the band structure of a crystal

In this tutorial, you will learn how to calculate the band structure of silicon by using the extended Hückel method.

Start VNL and create a new project

Open VNL and create a new project by clicking Create New. Give the project a Title (here: “Silicon_band_structure”), select the folder where data will be stored, then click OK and Open to start the project.

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Import the Silicon structure from the Database and send it to the Scripter

  1. In the VNL main window, click on the builder_icon icon to open the Builder.

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  2. Go to the Stash, click Add ‣ From Database, and choose Databases ‣ Crystals from the menu. Type “Silicon” in the filter field at the top and select “Silicon (alpha)” in the list. Click the plus_icon icon, or double-click its line in the list, to send it to the Stash.

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  3. Send the bulk structure to the script_generator_icon Scripter. In order to do that, click the sendto_icon button and choose Script Generator from the menu that appears.

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Set up the calculation and analyse the band structure

  1. In the Script Generator, use double-clicks to add a calculator_icon New Calculator block.

  2. Also add one analysis_icon Analysis ‣ Bandstructure block.

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  3. Change the default name of the NetCDF file in the Global IO options: Type in Si_band_structure.nc.

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  4. Double-click the calculator_icon New Calculator block to define the parameters for the quantum-chemical method:

    1. Set the calculator to “Extended Hückel” (or leave it at DFT if you so prefer), and specify a k-point sampling of nA = nB = nC = 13.
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    1. If you use the Extended Hückel, you must also change the basis set to Cerda.Silicon to get a proper description of the band gap.
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    1. Click OK to save the changes.
  5. Now open the Bandstructure block. We will not change anything, but you can see how the path in the face-centered cubic Brillouin zone between the symmetry points G, X, W, L, G, K, X, U, W, K, L, is set up. Click OK.

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  6. If you are interested in inspecting the actual Python script, you can now send the scipt to the editor_icon Editor: Use the sendto_icon button or simply drag and drop it onto editor_icon. Note that this will minimize the Script Generator window.

  7. In order to run the script, you simply send it to the job_manager_icon Job Manager, again using the sendto_icon button.

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  8. Save the script in the window that appears.

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  9. In the Job Manager, click jm_play_enabled_icon to run the script.

  10. When the script has finished (it should only take a few seconds), go back to the main VNL window, and click the tab (tab_icon) next to your NetCDF file, Si_band_structure.nc, to see the objects contained in it.

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  11. Select the Bandstructure object and plot it with the Bandstructure Analyzer in the right-hand plugins panel.

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  12. In the band structure plot that opens, you can zoom in using the zoomtorectangle_icon Zoom to rectangle tool. You can also save the figure by clicking the savefile_icon button.

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