You've activated the Raman+IR in-app guide.
In this guide, you will learn how to use the app to compute the Raman/IR spectra and dielectric properties (dielectric and Raman tensors, Born effective charges) of bulk silicon (Si).
Pre-requisite: This guide assumes that you already followed the Relaxation and electronic structure → Basic tutorial guide, or that you are already familiar with the app.
Click on Step 1: Select structure and follow the instructions to proceed.
In the structure selection step, we select the silicon structure from the examples.

Tasks

Warning: If the confirmed structure is not yet stored in the AiiDA database, it will be stored automatically when you proceed to the next step.
Warning: Changes after confirmation will reset the following steps.
In this second step (Configure workflow), we define the parameters needed to perform the calculation.

Tasks

  1. Select Full geometry, i.e. we optimize both cell parameters and atomic positions. This is important when computing phonons, as we are interested in the curvature of the energy at its minimum (i.e., where forces are zero).
  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.

Tasks

  1. Tick the Vibrational Spectroscopy (phonons) checkbox
  2. Open Step 2.2 for further instructions
Here we can customize the calculation parameters. The settings are divided into several tabs. Two tabs are always present: Additionally, each plugin activated in the previous step 2.1 can add additional tabs. Note that the app pre-configures defaults for most parameters.
See further instructions in the Basic settings panel below.
Here we define the basic settings of the simulations.

Tasks

  1. Since we are simulating silicon, select the Insulator electronic type
  2. Select the Fast protocol
  3. See further instructions in the Vibrational settings panel
Note: For the purpose of completing this guide in short time, we will use the Fast protocol for default parameters. However, you if dispose of enough computational resources, you can also select Balanced or Stringent.
In the Vibrational settings panel, we can customize the parameters for the Raman+IR calculation.

Tasks

Warning: Changes after confirmation will reset the following steps.

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. Select 1 node and 1 CPU for each of the codes below
  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.
Below you can monitor the status of the calculation, that might take several minutes to conclude even if we are using the fast protocol. Click on the Results panel. In the results panel, each tab will open results pertaining to a specific calculation submitted by the workflow.
See further instructions below in the Vibroscopy results tab.
When Raman/IR and dielectric results are available, the Load results button will become active in the corresponding tabs, allowing us to load the results from AiiDA.

Tasks

  1. Click on the Raman/IR spectra tab to visualize the Raman and infrared spectra.
  2. After having inspected the Raman/IR spectra tab, click on the Dielectric properties tab.
Below, there are the Raman/IR results.
Note: no active IR modes are detected, as follows from selection rules.

Tasks

  1. Inspect the Powder Raman spectrum.
  2. Change the Broadening to 50 cm-1 and click on the Update plot button.
  3. Inspect the animation of the Raman active modes (feel free to rotate the 3D view and check the animated arrows, indicating the oscillation direction and magnitude). We suggest to change the amplitude to 4 and to show a 2x2x2 supercell. Do different modes show different displacement?
  4. Go back to the Dielectric properties tab.
Dielectric properties are displayed below.

Tasks

  1. Inspect the three quantities represented in the tables: Dielectric, Raman tensors and Born effective charges.
  2. Use the Select atom site dropwdown to inspect the second Si atom.

Post-guide exercises

  1. Use the app to compute the Raman/IR spectra and dielectric properties of SiO2 (silicon oxide) and compare the results with the ones obtained for silicon. Check that, for SiO2, also some IR modes are active. In the Vibrational settings, select the same simulation type as used in this example.
  2. Use the app to compute both phonons dispersion and Raman/IR spectra of bulk silicon. In the Vibrational settings, select the "IR/Raman, Phonons, Dielectric, INS properties" simulation type. This will use a combined workflow to compute the phonon dispersion and the Raman/IR spectra in supercell approach.