Calculate Zero Point Energy¶
This page explains how to run a zero point energy calculation based on density functional theory. For the sake of this presentation, we will calculate the zero point energy for crystalline silicon in its equilibrium cubic-diamond crystal structure, making use of VASP as our simulation engine.
VASP version considered in this tutorial
The present tutorial is written for VASP at versions 5.3.5 or 5.4.4.
Create Job¶
Silicon in its cubic-diamond crystal structure is the default material that is shown on new job creation, unless this default was changed by the user following account creation. If silicon is still the default choice, it will as such be automatically loaded at the moment of the opening of Job Designer.
Choose Workflow¶
Workflows for calculating the Zero Point Energy through VASP can readily be imported from the Workflows Bank into the account-owned collection. This workflow can later be selected and added to the Job being created.
Examine Input File¶
The unique unit for this tutorial is the "vasp_zpe" unit. Clicking it will show the corresponding input files. The IBRION = 5 flag within the INCAR file enables VASP to run the displacements for the zero point energy calculation.
Set Sampling in Reciprocal Space¶
It is critical that a well-relaxed structure with converged k-point density is used for zero point energy calculations.
The default value of sampling, set according to KPPRA of 2000, is sufficient as can be verified by performing the relevant convergence study. When dealing with larger cells, setting k-grid dimensions through KPPRA should generally provide a reliable guess.
We explain how to perform both structural relaxations and k-points convergence studies in their respective tutorials.
Submit Job¶
Before submitting the Job, the user should click on the "Compute" tab of Job Designer and inspect the compute parameters included therein. Silicon is a small structure, so four CPUs and one minute of calculation runtime should be sufficient.
Examine Results¶
Once the Job execution is finished, switching to the Results tab of Job Viewer will show the results of the simulation, including a card titled "Zero Point Energy" that displays the value of this property for the material in question.
The larger its value, the more critical it becomes to include the zero point energy in ab-initio thermodynamic calculations performed at zero temperature.
Animation¶
We demonstrate the above-mentioned steps involved in the creation and execution of a Zero Point Energy computation workflow on silicon, using the VASP simulation engine, in the following animation.