FHI-gap

Official Resources

• Homepage: http://www.chem.pku.edu.cn/jianghgroup/codes/fhi-gap.html
• Source Repository: Available from authors (interfaced to WIEN2k)
• Documentation: http://www.chem.pku.edu.cn/jianghgroup/codes/fhi-gap.html
• License: As specified by authors (research code)

Overview

FHI-gap (Green's function with augmented plane waves) is an all-electron GW implementation based on the full-potential linearized augmented plane-wave plus local orbital ((L)APW+lo) method. Developed at the Fritz Haber Institute of the Max Planck Society and Peking University, it handles core, semicore, and valence states on the same footing, allowing correct treatment of core-valence interaction without relying on pseudopotential or frozen-core approximations.

FHI-gap is particularly valuable for systems with localized d- or f-electrons, where pseudopotential-based GW methods can be problematic. It implements G0W0 on top of LDA+U, enabling accurate treatment of strongly correlated d- and f-electron systems. The code is interfaced to the WIEN2k code for ground-state calculations, with an implementation into the EXCITING code also in progress. Test calculations demonstrate convergence behavior with respect to basis set size, k-points, frequency points, and unoccupied states.

Scientific domain: Many-body perturbation theory, all-electron GW, strongly correlated systems
Target user community: Researchers studying d- and f-electron materials with all-electron accuracy

Theoretical Methods

• All-electron GW (G0W0) implementation
• Full-potential (L)APW+lo method
• Correct treatment of core-valence interaction
• GW@LDA+U for strongly correlated systems
• Fourier interpolation for quasiparticle energies at arbitrary k-points
• No pseudopotential or frozen-core approximation

Capabilities (CRITICAL)

• All-electron GW quasiparticle energy calculations
• Full-potential LAPW treatment of all electronic states
• Correct core-valence interaction without pseudopotential approximation
• G0W0 on top of LDA+U for d- and f-electron systems
• Interface with WIEN2k for ground-state calculations
• Fourier interpolation for band structure on fine k-mesh
• Handles wide range of materials irrespective of composition

Inputs & Outputs

Input formats:

• WIEN2k ground-state calculation output
• k-point mesh and frequency grid specifications
• LAPW basis set parameters

Output data types:

• Quasiparticle energies on equally spaced k-mesh
• Band structure via Fourier interpolation
• Self-energy matrix elements
• Convergence test reports

Interfaces & Ecosystem

• Programming language: Fortran
• Ground-state code: WIEN2k (primary), EXCITING (in progress)
• Analysis tools: gap_analy and gap_gwnvf C-shell scripts for post-processing
• Fourier interpolation: Pickett et al. method for k-space interpolation

Limitations & Known Constraints

• Requires WIEN2k license for ground-state calculations
• Computationally expensive for all-electron treatment
• Research code with limited public distribution
• k-point convergence can be challenging
• Currently only G0W0 level implemented

Performance Characteristics

• All-electron treatment is more expensive than pseudopotential GW
• Core, semicore, and valence treated on same footing (no approximations)
• Fourier interpolation enables efficient band structure generation
• Convergence with basis set, k-points, and frequency grid required

Comparison with Other Codes

• vs VASP-GW: FHI-gap is all-electron (LAPW); VASP uses PAW/pseudopotentials. FHI-gap better for d/f systems
• vs ABINIT-GW: ABINIT uses pseudopotentials; FHI-gap avoids frozen-core issues
• vs BerkeleyGW: BerkeleyGW is pseudopotential-based standalone; FHI-gap is all-electron
• Unique strength: Correct all-electron treatment of core-valence interaction in GW

Best Practices

• Use G0W0@LDA+U for d- and f-electron systems with physical U values
• Carefully converge basis set size (product basis for wavefunction products)
• Use sufficient frequency points for imaginary axis integration
• Verify convergence with respect to unoccupied states
• Use Fourier interpolation for efficient band structure plotting

Verification & Sources

Primary sources:

1. FHI-gap page: http://www.chem.pku.edu.cn/jianghgroup/codes/fhi-gap.html
2. H. Jiang et al., Comput. Phys. Commun. 184, 348 (2013), DOI: 10.1016/j.cpc.2012.09.018
3. H. Jiang et al., Phys. Rev. B 82, 045108 (2010) - GW@LDA+U

Confidence: VERIFIED - Published in peer-reviewed journal with code page available