Official Resources
- Homepage: https://epw-code.org/
- Documentation: https://docs.epw-code.org/
- Source Repository: https://github.com/EPW-code/EPW (also part of QE distribution)
- License: GNU General Public License v2.0
Overview
EPW is a highly specialized code for calculating electron-phonon coupling and related properties from first principles using maximally localized Wannier functions. Part of the Quantum ESPRESSO distribution, EPW uses Wannier interpolation to achieve extremely efficient calculations of electron-phonon matrix elements on ultra-dense k and q-point grids, enabling accurate predictions of superconductivity, electrical transport, optical properties, and carrier mobilities.
Scientific domain: Electron-phonon coupling, superconductivity, transport properties
Target user community: Superconductivity researchers, transport properties, materials science
Theoretical Methods
- Electron-phonon coupling via Wannier interpolation
- Wannier function representation (from Wannier90)
- Eliashberg theory of superconductivity
- Migdal-Eliashberg equations
- Boltzmann transport for electrons and phonons
- Polar correction (Fröhlich interaction)
- Phonon-assisted optical absorption
- Temperature-dependent band structures
- Carrier mobility calculations
- Ultra-dense k/q-mesh interpolation
Capabilities (CRITICAL)
Category: Open-source electron-phonon code
- Electron-phonon matrix elements calculation
- Superconducting critical temperature (Tc)
- Eliashberg spectral function α²F(ω)
- Electron-phonon coupling constant λ
- Phonon linewidths from electron-phonon coupling
- Temperature-dependent electron self-energies
- Carrier mobility (electrons and holes)
- Electrical conductivity with electron-phonon scattering
- Seebeck coefficient
- Phonon-assisted optical absorption
- Polar materials (Fröhlich interaction)
- Anisotropic superconducting gaps
- Real-axis Eliashberg equations
- Ultra-fast Wannier interpolation
- Integration with Quantum ESPRESSO and Wannier90
- Production quality
Sources: Official EPW documentation, publications
Key Strengths
Wannier Interpolation:
- Ultra-dense k/q grids (millions of points)
- Orders of magnitude faster than direct DFT
- Smooth interpolation
- Production efficiency
- Accurate convergence
Superconductivity:
- Full Eliashberg theory
- Anisotropic gaps
- Critical temperature prediction
- Spectral functions
- Research and prediction
Transport Properties:
- Carrier mobility from first principles
- Electron-phonon scattering
- Temperature dependence
- Anisotropic tensors
- Thermoelectric properties
QE Integration:
- Seamless workflow
- Standard DFT input
- Wannier90 connection
- Production pipeline
Inputs & Outputs
-
Input formats:
- Quantum ESPRESSO DFT output
- Wannier90 Wannier functions
- EPW input file (epw.in)
- Phonon calculations from QE
-
Output data types:
- Electron-phonon matrix elements
- Eliashberg spectral function
- Superconducting Tc
- Carrier mobility
- Transport coefficients
- Self-energies
- Spectral functions
Interfaces & Ecosystem
Quantum ESPRESSO:
- Native integration
- Part of QE distribution
- Standard workflow
- pw.x and ph.x input
Wannier90:
- Essential for Wannier functions
- Wannier interpolation
- MLWFs for electrons
- Standard pipeline
Workflow:
- QE SCF/NSCF → QE phonons → Wannier90 → EPW
Workflow and Usage
Typical EPW Workflow:
# 1. DFT calculation (Quantum ESPRESSO)
pw.x < scf.in > scf.out
pw.x < nscf.in > nscf.out
# 2. Phonon calculation on coarse grid
ph.x < ph.in > ph.out
# 3. Wannierization (Wannier90)
wannier90.x -pp silicon
pw2wannier90.x < pw2wan.in
wannier90.x silicon
# 4. EPW calculation
epw.x < epw.in > epw.out
EPW Input Example (epw.in):
&inputepw
prefix = 'silicon'
amass(1) = 28.0855
outdir = './'
elph = .true.
kmaps = .false.
epbwrite = .true.
epbread = .false.
etf_mem = 1
nbndsub = 8
wannierize = .false.
num_iter = 500
iprint = 2
ephwrite = .true.
fsthick = 10.0
eptemp = 300
degaussw = 0.05
dvscf_dir = './save'
nkf1 = 40
nkf2 = 40
nkf3 = 40
nqf1 = 40
nqf2 = 40
nqf3 = 40
nk1 = 8
nk2 = 8
nk3 = 8
nq1 = 4
nq2 = 4
nq3 = 4
/
Advanced Features
Superconductivity:
- Migdal-Eliashberg equations
- Anisotropic Eliashberg (on Fermi surface)
- Real-axis solutions
- Critical temperature
- Gap functions
Transport:
- Carrier mobility (iterative BTE)
- Relaxation time approximation
- Electron-phonon scattering rates
- Temperature-dependent
- Anisotropic tensors
Polar Materials:
- Long-range Fröhlich interaction
- Polar optical phonons
- Quadrupole corrections
- LO-TO splitting
Optical Properties:
- Phonon-assisted absorption
- Indirect transitions
- Temperature-dependent spectra
Performance Characteristics
- Speed: Very fast via Wannier interpolation
- Accuracy: High-quality convergence
- k/q-mesh: Millions of points feasible
- Purpose: Electron-phonon specialist
- Typical: Hours to days (depending on convergence)
Computational Cost
- DFT/phonon calculations most expensive
- EPW interpolation very efficient
- Dense k/q-grid feasible
- Convergence testing important
- Production capable
Limitations & Known Constraints
- Requires QE+Wannier90: Part of workflow
- Wannier functions: Quality critical
- Phonon calculations: Expensive for large systems
- Learning curve: Steep, complex workflow
- Convergence: Many parameters to test
- Polar materials: Requires special treatment
- Documentation: Comprehensive but technical
- Imaginary modes: Can cause issues
Comparison with Other Codes
- Unique capability: Wannier interpolation for electron-phonon
- vs direct DFT: EPW orders of magnitude faster
- QE integration: Standard workflow
- Gold standard: For superconductivity/transport from first principles
Application Areas
Superconductivity:
- Tc prediction
- Conventional superconductors
- Anisotropic gaps
- Eliashberg theory
- Material discovery
Transport:
- Carrier mobility
- Semiconductors
- Thermoelectrics
- Electron-phonon scattering
- Temperature dependence
Optical Properties:
- Indirect absorption
- Phonon-assisted processes
- Temperature effects
- Spectroscopy theory
Best Practices
Workflow:
- Quality DFT convergence
- Good Wannier functions
- Phonon convergence
- Dense k/q-grid testing
- Systematic convergence
Wannier Functions:
- Appropriate projections
- Check spreads
- Band structure validation
- Energy window selection
Convergence:
- k-point and q-point grids
- Broadening parameters
- Temperature convergence
- Fermi surface sampling
Community and Support
- Open-source (GPL v2)
- Part of Quantum ESPRESSO
- Active development
- Mailing list
- Workshops and schools
- Comprehensive documentation
- Tutorial materials
Educational Resources
- EPW documentation
- QE schools tutorials
- Hands-on workshops
- Example calculations
- Publication list
- Theory background
Development
- Samuel Poncé (lead, Oxford)
- Quantum ESPRESSO developers
- International collaboration
- Active development
- Regular updates
- Feature additions
Research Impact
EPW is the standard tool for first-principles electron-phonon calculations, enabling accurate predictions of superconducting properties and carrier mobilities, cited in hundreds of publications.
Verification & Sources
Primary sources:
- Homepage: https://epw-code.org/
- Documentation: https://docs.epw-code.org/
- GitHub: https://github.com/EPW-code/EPW
- Publications: Comp. Phys. Comm. 209, 116 (2016); Rev. Mod. Phys. 89, 015003 (2017)
Secondary sources:
- Quantum ESPRESSO distribution
- Superconductivity literature
- Transport property papers
- User publications (hundreds)
Confidence: VERIFIED - Standard electron-phonon code
Verification status: ✅ VERIFIED
- Website: ACTIVE
- Documentation: COMPREHENSIVE
- Source: OPEN (GitHub, part of QE)
- License: GPL v2 (open-source)
- Category: Open-source electron-phonon code
- Status: Actively developed
- Community: Large, international
- Specialized strength: Wannier interpolation for electron-phonon coupling, superconducting Tc prediction, carrier mobility calculations, Eliashberg theory, ultra-dense k/q-mesh capability, Quantum ESPRESSO integration, production quality, gold standard for superconductivity and transport from first principles