Diamond Lattice Optimization and Phonons

This tutorial will show you how to:

  • Perform a geometry optimization (including lattice vectors optimization) for a periodic system
  • Calculate and visualize the phonon dispersion curves

More informations on these features can be found in the AMS User manual:

Set up the calculation

Let us begin by starting up the ADFInput GUI module:

1. Start ADFjobs
2. Click on SCM → New Input. This will open ADFInput
3. In ADFInput, select the DFTB panel: ADF → DFTB

Now we will import the diamond structure from our database:

1. Search for Diamond in the search box (magnifying glass)
2. Select Crystals → C

Phonons should be calculated for the optimal geometry. We therefore need to perform a geometry optimization:

In the Main panel
1. Select Task → Geometry Optimization
2. Select Followed by → Phonons

By default, only the internal degrees of freedom are optimized in a geometry optimization (i.e. the atomic positions within the unit cell are optimized, but the lattice vectors are not optimized). In order to obtain a proper phonon spectrum, one needs to optimize the lattice vectors as well as the internal degrees of freedom. When optimizing the geometry for a phonon calculation, we recommend using a strict Gradient Convergence threshold, e.g. 1.0E-4 Hartree/Angstrom.

1. Click on Details → Geometry Optimization
2. Tick the Optimize Lattice check-box
3. Set the Gradient Convergence threshold to 1.0E-4 Hartree/Angstrom

Optionally, you can tweak the settings of the phonon calculation in the panel Details → Phonons. Using a larger super cell in Details → Phonons will result in more accurate phonon curves, but will also significantly increase the computation time.

We will now set a few options specific to DFTB:

In the Main panel
1. Select K-Space Sampling → 5
2. Select Parameter Directory → DFTB.org/mio-1-1

Run the calculation

We are now ready to run the calculation.

1. Click on File → Save and name it “diamond_phonons”
2. Click on File → Run

This will open ADFjobs and start the calculation. You can monitor the progress of your calculation by opening the log file:

In ADFJobs:
1. right-click on your job and select logfile to see the log file
2. right-click on your job and select ADFMovie to monitor the progress of the geometry optimization
3. wait for the calculation to finish...

Visualize the Phonons

Once the calculation is completed, you can visualize the phonon dispersion curves:

In ADFJobs, right-click on your job and select BandStructure

This will open the BandStructure visualization program:


You can visualize the motion of the atoms for certain modes (marked by a blue dot in the dispersion curves):

Click on one of the “Modes” dots in the phonon dispersion curves

You can also visualize the electronic band structure and density of states computed by DFTB:

In the BandStructure module, click on Options → BandStructure

Thermodynamic properties derived from the phonon calculation are printed to the output file. To open the output file:

In ADFJobs, right-click on your job and select Output
In ADFOutput, search for “Thermo”