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 ADFinput1. Switch to DFTB2. 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 4.0Click 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 52. Select the ‘DFTB.org/3ob-3-1’ parameter set3. Click on ... next to GeometryOptimization to go to the Geometry Optimization options panel4. 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 → RunWhile the optimization is running, you can watch the progress by clicking SCM → MovieWhen 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)
DFTB documentation: Periodic
Step 4: Phonons¶
- Activate the ADFinput window of the DFTB-Diamond inputSelect “Phonons” as TaskFile → Save as..., use “DFTB-Diamond_phonons” as filenameFile → RunWhen 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.
For the study of phonons isotopic shift see the AtomMasses key.