Official Resources
- Repository: https://github.com/respack-dev/wan2respack
- RESPACK Homepage: https://sites.google.com/view/kazuma7k6r/respack
- License: GNU General Public License v3.0
Overview
Wan2respack is a critical interface utility that bridges Wannier90 and RESPACK. It converts the maximally localized Wannier functions (MLWFs) generated by Wannier90 into the specific input format required by RESPACK. This enables RESPACK to perform advanced many-body calculations—specifically the Constrained Random Phase Approximation (cRPA)—on models derived from standard DFT codes (like Quantum ESPRESSO) via Wannierization. It effectively allows for the ab initio derivation of effective Hamiltonian parameters (Hubbard $U$, Hund's $J$, and inter-site $V$) for strongly correlated materials.
Scientific domain: Strongly Correlated Electrons, Effective Hamiltonians, Downfolding
Target user community: Researchers using DFT+DMFT or needing accurate interaction parameters for lattice models
Theoretical Methods
- Basis Transformation: Converts the real-space Wannier Hamiltonian and orbital definitions from Wannier90 conventions to RESPACK's internal format.
- Downfolding: Facilitates the construction of low-energy effective models by preparing the detailed full-frequency data for cRPA.
- Constrained RPA (cRPA): Prepares inputs for the calculation of the frequency-dependent screened Coulomb interaction $W(\omega)$ by screening the bare Coulomb interaction $v$ within the RPA, excluding the target subspace.
Capabilities
- Format Conversion:
- Reads
case_hr.dat, case.chk, or case.mmn/case.amn (depending on workflow versions).
- Writes RESPACK Hamiltonian and overlap files.
- Workflow enabling:
- Enables the calculation of static and frequency-dependent Hubbard parameters.
- Supports microscopic derivation of model parameters for customized tight-binding models.
Key Strengths
- Interoperability: Connects the vast ecosystem of codes supporting Wannier90 (QE, VASP, Abinit) to the specialized response function capabilities of RESPACK.
- Automation: Automates the often error-prone manual conversion of basis set definitions.
- Open Source: Freely available and modifiable under GPLv3.
Inputs & Outputs
- Inputs:
- Wannier90 output files (
_hr.dat, _centres.xyz, _u.mat or checkpoint).
- Quantum ESPRESSO / DFT data (if wavefunctions are needed for matrix elements).
- Outputs:
- RESPACK-compatible Hamiltonian (
dat.hamiltonian).
- Overlap matrices (
dat.overlap).
- Lattice and orbital information.
Interfaces & Ecosystem
- Upstream:
- Quantum ESPRESSO: Typical source of Bloch states.
- Wannier90: Generates the MLWFs.
- Downstream:
- RESPACK: Calculates dielectric functions and screened interactions using the converted data.
Performance Characteristics
- Computational Cost: Negligible compared to the preceding DFT/Wannier steps and the subsequent response function calculation.
- Memory: Low memory footprint (manipulates small tight-binding matrices).
Limitations & Known Constraints
- Dependency Chain: Strict reliance on the formats of specific Wannier90 versions; updates to Wannier90 outputs may require updates to wan2respack.
- Non-Standard Basis: Does not check the physical validity of the Wannier functions; the user must ensure MLWFs are well-localized and symmetric.
Comparison with Other Codes
- vs. cRPA in VASP/Abinit: Some DFT codes have internal cRPA implementations; Wan2respack + RESPACK allows for a modular approach where the Wannierization (basis construction) is decoupled from the screening calculation.
- vs. TRIQS cRPA: TRIQS also offers cRPA tools; RESPACK is another alternative often favored by the Japanese computational materials science community (ISSP).
Application Areas
- Hubbard Models: Deriving $U$ and $J$ for cuprates, iron pnictides, and ruthenates.
- Molecular Solids: Calculating intermolecular screening parameters.
- Excitonic Physics: Inputs for Bethe-Salpeter calculations in localized bases.
Community and Support
- Development: Maintained by the RESPACK development team (Kazuma Nakamura et al., Kyushu Institute of Technology / ISSP).
- Documentation: Provided within the repository and RESPACK website.
Verification & Sources
- Repository: https://github.com/respack-dev/wan2respack
- Primary Publication (for RESPACK/Method): K. Nakamura et al., Phys. Rev. B 80, 125102 (2009).
- Verification status: ✅ VERIFIED
- Active interface tool.
- Essential for the RESPACK workflow.