Calculate Zero Point Energy

This tutorial explains how to calculate the zero point energy of crystalline silicon in its equilibrium cubic-diamond crystal structure using Density Functional Theory (DFT) with VASP.

VASP version

This tutorial applies to VASP versions 5.3.5, 5.4.4, 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 the Zero Point Energy calculation with VASP 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. Examine the input file

The single unit for this calculation is "vasp_zpe". Clicking it reveals the corresponding input files. The IBRION = 5 flag within the INCAR file enables VASP to run the atomic displacements required for the zero point energy calculation.

4. Set sampling in reciprocal space

A well-relaxed structure with converged k-point density is critical for zero point energy calculations.

The default sampling (KPPRA of 2000) is sufficient, as can be verified by performing a convergence study. For larger cells, setting k-grid dimensions through KPPRA generally provides a reliable starting point.

Instructions for structural relaxations and k-point convergence studies are available in their respective tutorials.

5. Submit the job

Before submitting the job, review the Compute tab of Job Designer to verify the compute parameters. Silicon is a small structure, so 4 CPUs and 1 minute of runtime are sufficient.

6. Examine the results

Once the job completes, the Results tab of Job Viewer displays a "Zero Point Energy" card with the calculated value. The larger this value, the more important it becomes to include zero point energy in ab-initio thermodynamic calculations performed at zero temperature.

7. Video walkthrough

The animation below demonstrates the full zero point energy workflow on silicon using VASP.