Official Resources
- Homepage: https://www.flapw.de/spex/
- Documentation: https://www.flapw.de/spex/documentation/
- Source Repository: https://github.com/flapw-spex/spex
- License: Free for academic use
Overview
Spex is an all-electron code for calculating quasiparticle energies and optical spectra using many-body perturbation theory (GW and Bethe-Salpeter equation). Developed primarily at Forschungszentrum Jülich, Spex uses the FLAPW method as input and implements sophisticated algorithms for GW self-energy and BSE kernel calculations. It is particularly powerful for accurate band gaps, quasiparticle band structures, and optical absorption spectra of solids.
Scientific domain: GW approximation, BSE, optical spectra, all-electron MBPT
Target user community: Spectroscopy researchers, solid-state physicists, FLAPW users
Theoretical Methods
- GW approximation (G₀W₀, GW₀, self-consistent GW)
- Bethe-Salpeter Equation (BSE)
- Random Phase Approximation (RPA)
- All-electron implementation
- FLAPW basis (uses FLEUR output)
- Full-frequency integration
- Contour deformation
- Plasmon-pole models
Capabilities (CRITICAL)
- Quasiparticle energies (GW)
- Accurate band gaps
- Quasiparticle band structures
- Optical absorption spectra (BSE)
- Exciton binding energies
- Dielectric functions
- Photoemission spectra
- All-electron accuracy
- Core-level excitations
- Finite momentum transfer
- FLAPW input compatibility
- Production quality
Sources: Spex website (https://www.flapw.de/spex/)
Key Strengths
All-Electron GW:
- Full treatment of all electrons
- No pseudopotential approximations
- Core states included
- High accuracy
- Benchmark quality
FLAPW Integration:
- Uses FLEUR output
- FLAPW basis advantages
- Full-potential accuracy
- All-electron wavefunctions
- Systematic approach
Advanced Algorithms:
- Full-frequency GW
- Contour deformation
- Efficient RPA
- Optimized implementations
- Production performance
Optical Spectra:
- BSE for excitons
- Accurate absorption
- Binding energies
- Oscillator strengths
- Experimental comparison
Spectroscopy Focus:
- Photoemission (PES/IPES)
- Optical absorption
- Core-level excitations
- Finite momentum
- Comprehensive spectra
Inputs & Outputs
-
Input formats:
- FLEUR wavefunctions and densities
- Spex input files
- k-point meshes
- Frequency grids
-
Output data types:
- Quasiparticle energies
- Band structures
- Spectral functions
- Optical spectra
- Dielectric functions
- BSE eigenstates
Interfaces & Ecosystem
-
FLEUR Interface:
- Primary DFT input
- FLAPW wavefunctions
- Seamless integration
- Tested workflow
-
Visualization:
- Standard plotting tools
- Spectral data output
- Band structure formats
Workflow and Usage
Typical Workflow:
- Run FLEUR DFT calculation
- Prepare Spex input
- Run GW calculation
- Analyze quasiparticle energies
- Optional: Run BSE for optics
- Extract and visualize spectra
GW Calculation:
spex input.spex
# Computes GW corrections
BSE for Optics:
- Calculate RPA dielectric function
- Solve BSE for excitons
- Obtain optical absorption spectrum
Advanced Features
GW Variants:
- G₀W₀ (one-shot)
- GW₀ (partially self-consistent)
- Self-consistent GW
- Different approximations
- User control
Frequency Integration:
- Full-frequency approach
- Contour deformation
- Accurate self-energy
- No plasmon-pole approximation
- Systematic convergence
BSE Implementation:
- Electron-hole interaction
- Exciton eigenstates
- Binding energies
- Oscillator strengths
- Finite momentum transfer
All-Electron:
- Core electrons included
- Core-level excitations
- High-energy spectroscopy
- No frozen-core approximation
- Complete treatment
Performance Characteristics
- Speed: Moderate (all-electron MBPT)
- Accuracy: Excellent (all-electron)
- System size: Unit cell to moderate
- Scaling: Standard GW scaling
- Typical: Research calculations
Computational Cost
- GW: More expensive than DFT
- BSE: Additional cost for optics
- All-electron: Higher cost than pseudopotential
- Accuracy: Justifies computational expense
- Production: Feasible for research
Limitations & Known Constraints
- FLEUR dependency: Requires FLEUR DFT input
- System size: Limited to moderate systems
- Learning curve: MBPT expertise needed
- Computational cost: All-electron expense
- Platform: Linux systems
Comparison with Other Codes
- vs BerkeleyGW: Spex all-electron, BerkeleyGW pseudopotential
- vs Yambo: Both GW/BSE, Spex FLAPW-based
- vs exciting: Both all-electron, different algorithms
- Unique strength: FLAPW-based all-electron GW/BSE, full-frequency, FLEUR integration
Application Areas
Band Gap Corrections:
- Accurate fundamental gaps
- Quasiparticle bands
- Semiconductor properties
- Insulator gaps
- Band structure refinement
Optical Spectroscopy:
- Absorption spectra
- Exciton physics
- Optical gaps
- Oscillator strengths
- Experimental comparison
Photoemission:
- PES/IPES spectra
- Spectral functions
- Satellite features
- Comparison with experiments
Materials Science:
- Electronic structure
- Excited states
- Optical properties
- Spectroscopy interpretation
Best Practices
DFT Preparation:
- Converged FLEUR calculation
- Appropriate k-mesh
- Sufficient empty states
- Quality wavefunctions
GW Convergence:
- k-point convergence
- Frequency grid
- Empty states
- Cutoff parameters
- Systematic testing
BSE Calculations:
- Appropriate transitions
- k-point sampling
- Exciton convergence
- Numerical parameters
Community and Support
- Free for academic use
- FLAPW community
- Documentation available
- Research group support
- Publications and tutorials
Educational Resources
- Spex documentation
- FLAPW school materials
- GW/BSE tutorials
- Published papers
- User examples
Development
- Forschungszentrum Jülich
- Christoph Friedrich (main developer)
- Active development
- Regular updates
- Research-driven improvements
Research Applications
- Accurate band gaps
- Optical spectra
- Quasiparticle physics
- Exciton studies
- Spectroscopy theory
Technical Innovation
All-Electron MBPT:
- No pseudopotentials
- Core states included
- Complete accuracy
- Benchmark calculations
FLAPW Basis:
- Full-potential advantages
- Systematic basis
- All-electron treatment
- High precision
FLAPW-GW Synergy
- FLEUR DFT input
- FLAPW wavefunctions
- All-electron consistency
- Integrated workflow
- Production quality
Verification & Sources
Primary sources:
- Spex website: https://www.flapw.de/spex/
- GitHub: https://github.com/flapw-spex/spex
- C. Friedrich et al., Comp. Phys. Comm. (2011)
- Documentation and user manual
Secondary sources:
- GW/BSE method literature
- FLAPW method papers
- Spectroscopy calculations
- Application publications
Confidence: CONFIRMED - Established research code
Verification status: ✅ VERIFIED
- Website: ACCESSIBLE
- GitHub: Available
- Documentation: Comprehensive
- Community support: FLAPW/Jülich groups
- Active development: Regular updates
- Specialized strength: All-electron GW/BSE, FLAPW integration, full-frequency approach, optical spectra, photoemission, core excitations, benchmark accuracy