Exporting Data for DFT

Exporting Data for DFT

MatCraft makes it easy to download crystal structures ready for DFT calculations. This tutorial covers exporting structures and preparing input files for VASP and Quantum ESPRESSO.

Exporting from the Web UI

Single material:

1. Open the material detail page
2. Click Download on the Structure tab
3. Choose CIF, POSCAR, or XYZ format

Batch export from search results:

1. Run a search with your desired filters
2. Check the materials you want to export
3. Click Export Selected and choose the format
4. A ZIP file downloads containing all structure files

Using the API for Bulk Export

For high-throughput screening, use the Python SDK:

from matcraft import MatCraftClient

client = MatCraftClient()

# Search for stable binary nitrides
materials = client.search(
    elements=["N"],
    n_elements_max=2,
    e_above_hull_max=0.05,
    limit=50
)

# Export all as POSCAR
for mat in materials:
    mat.export("poscar", path=f"structures/{mat.formula}_{mat.material_id}.vasp")
    print(f"Exported {mat.formula}")

Preparing VASP Input Files

The exported POSCAR is ready for VASP. You still need to create:

INCAR (calculation parameters):

ENCUT = 520
EDIFF = 1E-6
ISMEAR = 0
SIGMA = 0.05
IBRION = 2
NSW = 100
ISIF = 3

KPOINTS (k-mesh):

Automatic mesh
0
Gamma
6 6 6
0 0 0

POTCAR: Assemble from your VASP pseudopotential library based on the elements in the POSCAR.

Preparing Quantum ESPRESSO Input

Convert the CIF file to QE format using cif2cell or the ASE toolkit:

from ase.io import read, write

atoms = read("Si_mp-149.cif")
write("Si.pwi", atoms, format="espresso-in",
      pseudopotentials={"Si": "Si.pbe-n-rrkjus_psl.1.0.0.UPF"},
      input_data={
          "system": {"ecutwfc": 60, "ecutrho": 480},
          "electrons": {"conv_thr": 1e-8},
      },
      kpts=(6, 6, 6))

Tips for DFT Calculations

• Relax first: Always run a geometry optimization before computing properties, even for structures from well-converged databases
• Check convergence: Test ENCUT and k-point mesh convergence for your specific system
• Magnetic materials: Set ISPIN=2 and initial magnetic moments for transition metal compounds
• Band gaps: Use HSE06 or GW methods for accurate band gaps; GGA/PBE systematically underestimates
• Large cells: For supercells or surfaces, reduce k-point density proportionally

Jupyter Notebook Export

For reproducible workflows, export a Jupyter notebook that includes the complete pipeline from data retrieval to VASP input file preparation.