Periodic DFTB, Lattice Optimization, DOS, band structure and phonons¶

Step 1: Lattice optimization - input setup¶

To perform geometry optimization of a lattice, we will start from a diamond crystal with incorrect lattice values, and let DFTB optimize this value. Next, we will proceed to display additional information obtained during the evaluation.

Start ADFinput

Select the DFTB panel: panel bar ADF → DFTB

Choose Bulk to enable periodicity.

Click the structure tool (the snowflake next to the X tool),

Choose Cubic → Diamond

Set the lattice parameter parameter a to 6.0 and click OK

Click the Details button (...) for the GeometryOptimization task

Check the Optimize Lattice box

Go to the Main panel

Make sure model is set to DFTB, and that the Dresden parameter set is selected (normally you would want to use better parameters like the included 3OB set)

Choose File → Save as... and save the input as “DFTB-Diamond”.

Step 2: Lattice optimization - execution¶

File → Run.

While the optimization is running, you can watch the progress by clicking SCM → Movie

When asked to read the new coordinates (when the calculation finishes), click Yes

From the movie, you can observe how the unit cell shrinks as it is optimized.

Step 3: DOS and Band Structure¶

You can visualize the density of states (DOS) directly from the converged optimization.

SCM → DOS (in the ADFmovie or ADFinput window)

Similarly, you can visualize the band structure

SCM → Band Structure

Step 4: Phonons¶

Activate the ADFinput window with the DFTB-Diamond input

Select “Phonons” as Task

File → Save as..., use “DFTB-Phonons” as filename

File → Run

When completed: use SCM → Band Structure in the ADFtail window (showing the logfile)

A window will appear showing the phonons diagram. Clicking on the curves at the location of the vertical red bars will show the actual crystal vibrations.