Si bandstructure issues

Hi all! This is my first post on matsci.org, so my apologies if I’m missing anything.

I recently set up Atomate, and I’m running a bandstructure workflow with Si to test my configuration. Here’s the script I’m using to add the workflow:

from pymatgen.core import Structure
from fireworks import LaunchPad
from atomate.vasp.workflows.presets.core import wf_bandstructure

struct = Structure.from_file(*path to Si POSCAR*)
wf = wf_bandstructure(struct)
lpad = LaunchPad.auto_load()
lpad.add_wf(wf)

This seems to run without error. Lattice parameters are reasonable, energy looks well converged, though I am getting higher stresses in the nscf line calculation (50 kbar diagonal, 10 kbar off-diagonal).

The band gap roughly matches the Materials Project value (0.62 vs. 0.61 eV), but my band structure does not resemble the Si bandstructure (mine has direct band gap, X point very different shape).

I’m plotting the bandstructure using this script, provided in the atomate tutorial:

from atomate.vasp.database import VaspCalcDb
from pymatgen.electronic_structure.plotter import DosPlotter, BSPlotter

atomate_db = VaspCalcDb.from_db_file(*PATH_TO_MY_DB_JSON*)

line_bs_entry = atomate_db.collection.find_one({'task_id':17})
bandstructure = atomate_db.get_band_structure(line_bs_entry['task_id'])
bs_plotter = BSPlotter(bandstructure)
bs_plotter.get_plot()

Any ideas why this might be happening? Thank you :]

Hi @KatNykiel,

Welcome! No apologies needed, there’s a lot to learn.

My first guess – is your structure in its primitive setting?

Ideally, to calculate a band structure you would first use SpacegroupAnalyzer like so:

from pymatgen.symmetry.analyzer import SpacegroupAnalyzer
sga = SpacegroupAnalyzer(struct)
struct = sga.get_primitive_standard_structure()

This follows the convention of Setyawan and Curtarolo.

If you do not do this, you may have misleading labels, or band folding if you use a supercell – and this can make indirect transitions look direct.

Perhaps this is something else, but this was my first thought!

Hope this helps,

Matt

1 Like

Matt,

Thank you for your help! You were right, I wasn’t using the primitive unit cell. I re-submitted the workflow with SpacegroupAnalyzer and obtained a more reasonable bandstructure.

Thanks!

Kat

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Very glad to hear it! Good luck :slight_smile: