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

This tutorial will walk through the use of periodic DFTB to optimize the lattice parameters. The density of states and band structure of the optimized structures will be displayed.

Step 1: Lattice optimization - input setup¶

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

: Start ADFinput

1. Switch to DFTB

2. Choose Bulk to enable periodicity.

3. Click the structure tool (the snowflake), and chose Cubic → Diamond

: In the dialog window, set the lattice parameter a to 4.0

Click OK

You should now have a diamond crystal with a too-large lattice:

We will now set up the DFTB simulation parameters:

: 1. Set the K-Space sampling to 5

2. Select the ‘DFTB.org/3ob-3-1’ parameter set

3. Click on ... next to GeometryOptimization to go to the Geometry Optimization options panel

4. In the Geometry Optimization panel tick the Optimize lattice option

Step 2: Lattice optimization - execution¶

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

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: Band Structure and DOS¶

You can visualize the Band structure and density of states (DOS) of the converged geometry:

: SCM → BandStructure (in the ADFmovie, ADFinput or ADFJobs window)

Step 4: Phonons¶

: Activate the ADFinput window of the DFTB-Diamond input

Select “Phonons” as Task

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

File → Run

When completed: use SCM → Band Structure to visualize the phonon dispersion curves

Clicking on the curves at the location of the vertical red bars will show the crystal vibrations.