Phonon Dispersions and Density of States Calculation

This tutorial explains how to calculate the Phonon Dispersion Curves and Phonon Density of States of crystalline silicon in its cubic-diamond crystal structure using Density Functional Theory (DFT) with Quantum ESPRESSO.

Quantum ESPRESSO version

This tutorial applies to Quantum ESPRESSO versions 5.2.1, 5.4.0, 6.0.0, 6.3, and later.

1. Create the job

Silicon in its cubic-diamond crystal structure is the default material loaded on new job creation, unless the default was changed after account creation.

2. Select the workflow

Workflows for phonon calculations with Quantum ESPRESSO can be imported from the Workflows Bank into the account-owned collection. The workflow can then be selected and added to the job being created.

3. Set sampling in reciprocal space

A high q-point density is critical for resolving phonon dispersion details.

The phonon workflow contains multiple units. The first unit configures the self-consistent calculation of energy eigenvalues and wave functions. Subsequent units are described in the theoretical explanation in Ref. [^1] of this page.

Set the q-point grid to 3 × 3 × 3 under Important Settings. Also reduce the k-point grid from its default to 6 × 6 × 6 to make the q- and k-point grids commensurate and reduce computational cost.

The associated i-grid for reciprocal/real-space transformation and interpolation should be set to 18 × 18 × 18. The recommended q-point path should also be applied to sample the vibrational states across the Brillouin Zone.

4. Submit the job

Before submitting the job, review the Compute tab of Job Designer to verify the compute parameters.

Computational cost

Phonon calculations are computationally demanding. Despite silicon being a small structure, the settings above require at least 45 minutes on 16 compute cores.

5. Examine the results

Once all units complete, the Results tab of Job Viewer displays the phonon dispersion curves and the Phonon Density of States (directly above the dispersion curve).

6. Video walkthrough

The animation below demonstrates the full phonon calculation workflow on silicon using Quantum ESPRESSO.