TB2J Skill

This skill provides expert guidance on using the TB2J package to calculate magnetic interaction parameters (Heisenberg exchange $J$, DMI $D$, Anisotropy $J_{ani}$) from DFT inputs.

References

• Command Reference: Detailed flags and arguments for all scripts (wann2J.py, siesta2J.py, etc.).
• Workflows & DFT Prep: Step-by-step guides for preparing VASP/Wannier90/Siesta inputs.
• Conventions: Vital information on Hamiltonian signs, units, and spin normalization.
• Outputs: Explanations of exchange.out, exchange.xml, and interfaces to Vampire/Multibinit.

Common Workflows

1. Wannier90 (VASP, QE, Abinit)

• Command: wann2J.py
• Key Step: Ensure projections in .win file cover magnetic orbitals.
• See: Workflows > Wannier90

2. Siesta

• Command: siesta2J.py
• Key Step: Set SaveHS True in .fdf.
• See: Workflows > Siesta

3. Abacus

• Command: abacus2J.py
• Key Step: Set out_mat_hs2 1 in INPUT.
• See: Workflows > Abacus

4. Non-Collinear / Anisotropy

• Option A: Full non-collinear DFT + wann2J.py --spinor.
• Option B: "Rotate and Merge" using TB2J_rotate.py (generate structures) -> DFT -> TB2J_merge.py (combine results).
• See: Workflows > Non-Collinear

Troubleshooting / FAQ

• Results contradict experiment?

  • Check Conventions. Are you comparing $J$ vs $2J$?
  • Verify the Fermi Energy (--efermi) matches the DFT calculation exactly.
  • Is the system metallic? Try increasing K-mesh or adjusting --nz.

• Wannier functions not localized?

  • Check wannier90.wout for spreads.
  • Adjust dis_win (outer window) to include all relevant bands.
  • Check projections.

• "Orbitals not found" error?

  • Ensure --elements matches the atoms in the structure file.
  • Check if exclude_orbs is needed for semi-core states.