In this guide, you will learn how to model ferromagnetic materials and how to include Hubbard U corrections in your calculations. In this example, you will investigate the PDOS of CoO and analyze how the Hubbard U influences the electronic structure.
Click on Step 1: Select structure and follow the instructions to proceed.

Tasks

  1. Click on the From examples tab
  2. Click on Simple crystals
  3. Select Cobalt oxide from the dropdown list
  4. Click the Confirm button to proceed

Tasks

  1. Select Structure as is (in the interest of time, we skip the relaxation here)
  2. Open step 2.1 for further instructions
Here we select the properties to calculate. Each property is associated with a workflow that will submit one or more calculations. In this guide, we will analyze the PDOS, since this will facilitate the understanding of the impact of the Hubbard U on the electronic structure.

Tasks

  1. Check (activate) Electronic projected density of states (PDOS)
  2. Open step 2.2 for further instructions
Note: If running locally (for example, on the AiiDAlab demo server), we recommend selecting the fast protocol to reduce the computational cost.

Tasks

  1. Select the fast protocol
  2. Set Magnetism to On. Keep the Electronic type as metal (this is required since we want to determine the magnetization self-consistently. When setting to insulator, the app will inform you that this is only possible for claculations for which you fix the total magnetization of the unit cell.).
  3. Open the Advanced settings panel to set the initial magnetic moments and the Hubbard U values.
Here, we will define the initial magnetic moments and set the Hubbard U values.

Tasks

Setup ferromagnetism
When Magnetism is activated, the Magnetization subsection appears below. In this tutorial, you will set the Initial magnetic moments of the different elements. Note: In general, it is also possible to set the Total magnetization instead.
  1. Set the initial magnetic moments (replacing the default ones) of Co to 3 μB and O to 0.6 μB.
Setup DFT+U
  1. Enable Hubbard-U corrections by activating the Define U values checkbox.
  2. Define the U values for the different elements. Set U for Co - 3d to 6 eV (we do not apply a U correction to O).
  3. Switch to the PDOS tab for some final fine-tuning

Tasks

  1. Set Energy grid step (eV) to 0.03 eV. We change this parameter here to reduce the computational costs.
  2. Click the Confirm button to proceed

In the submission step, we define the computational resources to be used in the calculations. The global resources are used to define resources across all workflow calculations. Optionally, you can override the resource settings for specific calculations.

Warning: If running locally (for example, on the AiiDAlab demo server), we recommend keeping nodes and CPUs at the default minimum of 1 each.

Once the resources are defined, we can optionally customize the workflow label (pre-filled according to the settings of steps 1 & 2), as well as provide a detailed description of the workflow. Once we are ready, we can submit the workflow. You first need to select which code (code executable + computer where this will run) to use for each step of the workflow. The Quantum ESPRESSO app should always install a local Quantum ESPRESSO executable that is sufficient for this tutorial, but you can setup additional codes installed on remote supercomputers. For more information on how to set up codes, please refer to the corresponding documentation.

Tasks

  1. Check that the the default options in the "Global resources" panel are the expected ones. Specifically: select 1 node and 1 CPU for each of the codes. Unless you want to run elsewhere, use the default codes on the AiiDAlab server (ending with `@localhost`) that are available from the dropdown menus.
  2. (Optional) customize the workflow label
  3. (Optional) add a workflow description
  4. Click the Submit button to proceed
Warning: The workflow may take a moment to submit.
Here in the results panel, each tab will open results pertaining to a specific calculation submitted by the workflow.
See further instructions below in the Electronice PDOS tab.
When results are available, the Load results button will become active allowing us to load the results from AiiDA.

Tasks

  1. Once the calculation is complete, click on the Load results button to load the available results
  2. Select Group by element (atomic species) in Atomic grouping to get a top-level understanding of the electronic structure.
  3. Next, focus on the specific orbitals of Co in the spin-down channel. Select Group by angular momentum in Orbital grouping. Understand where the Co-3d (spin-down) states are located. To do so, double click on the Co-3d (spin-down) states in the legend. This will hide all the other states. To deselect, simply double click again.
  4. If you want to go in more detail, select No grouping (each orbital separately) in Orbital grouping. This will show you the contributions of all individual orbitals.

Post-guide exercises

  1. Follow the steps in the guide again, but this time, unset the Hubbard U or set it to 0.
    • What do you notice?
    • What happens to the electronic states around the Fermi level?
  2. Optionally: Follow the same steps as before, but this time, choose a different U value. Inspect the results and see how the U values influence the electronic structure.
We already provide some of these results in our examples. Check the Download examples on the landing page of the app. You can follow the instructions there to import the examples. Afterwards, you can inspect the results in your Calculation history.