VASP-GW

Official Resources

• Homepage: https://www.vasp.at/
• Documentation: https://www.vasp.at/wiki/Practical_guide_to_GW_calculations
• License: Commercial (VASP license required)

Overview

The GW approximation module in VASP (Vienna Ab initio Simulation Package) implements many-body perturbation theory calculations for computing quasiparticle energies and band gaps. Available since VASP 5.x, the GW module is one of the most widely used implementations of the GW method for realistic materials, providing access to spectral properties through the determination of quasiparticle energies.

The GW method approximates the self-energy as the product of the Green's function G and the screened Coulomb interaction W, derived from Hedin's equations by neglecting vertex corrections. VASP offers multiple GW flavors including single-shot G0W0, partially self-consistent EVGW0 (eigenvalue self-consistent with fixed W), and QPGW0 (quasi-particle self-consistent with updated W). The implementation uses the random phase approximation (RPA) for the dielectric matrix and supports both plasmon-pole models and full frequency integration.

Scientific domain: Many-body perturbation theory, quasiparticle band structure
Target user community: Computational materials scientists requiring accurate band gaps

Theoretical Methods

• GW approximation to Hedin's equations
• G0W0 (single-shot quasiparticle energies)
• EVGW0 (eigenvalue self-consistent GW with fixed W)
• QPGW0 (quasi-particle self-consistent with updated screening)
• COHSEX approximation (static screening)
• RPA dielectric matrix computation
• Plasmon-pole and full frequency integration
• k·p perturbation theory for dielectric matrix head/wings

Capabilities (CRITICAL)

• Quasiparticle energy calculations for band gaps
• Multiple self-consistency levels (G0W0, EVGW0, QPGW0)
• Spectral and non-spectral frequency integration methods
• Dielectric matrix computation in RPA
• Supports plane-wave PAW and pseudopotential frameworks
• k-point convergence acceleration via k·p perturbation theory
• Frequency-dependent dielectric function output
• Integration with VASP ground-state and BSE modules

Inputs & Outputs

Input formats:

• VASP INCAR files with ALGO tags for GW (ALGO=GW0, EVGW0, QPGW0, etc.)
• WAVECAR from preceding DFT calculation
• WAVEDER for k·p dielectric matrix (LOPTICS=.TRUE.)

Output data types:

• Quasiparticle energies and band gaps
• Self-energy matrix elements
• Screened Coulomb interaction W
• Dielectric matrix files (Wxxxx.tmp)
• Frequency-dependent dielectric function

Interfaces & Ecosystem

• Programming language: Fortran (VASP core)
• Prerequisite: VASP DFT ground-state calculation
• Downstream: BSE calculations using GW output
• Parallel computing: MPI parallelization
• Part of VASP suite: Integrated with DFT, BSE, and RPA modules

Limitations & Known Constraints

• Commercial VASP license required
• Computationally expensive (quartic scaling for full frequency)
• Limited to relatively small unit cells for full frequency integration
• G0W0 results depend on DFT starting point
• Core-valence interaction approximated in pseudopotential framework

Performance Characteristics

• Quartic scaling O(N^4) for spectral method
• Spectral method (LSPECTRAL=.TRUE.) is default and efficient
• Memory-intensive for large dielectric matrices
• k-point convergence can be slow for insulators/semiconductors
• VASP 6.0+ supports GW in one go (no two-step requirement)

Comparison with Other Codes

• vs FHI-gap: FHI-gap uses all-electron LAPW; VASP uses PAW/pseudopotentials
• vs ABINIT-GW: ABINIT is open-source; VASP is commercial. Both offer G0W0 and self-consistent GW
• vs BerkeleyGW: BerkeleyGW is standalone post-processing; VASP-GW is integrated
• vs Yambo: Yambo works with QE/ABINIT output; VASP-GW is self-contained

Best Practices

• Use LOPTICS=.TRUE. in DFT step to generate WAVEDER for k·p corrections
• Converge NOMEGA, ENCUTGW, and NBANDS carefully
• Use EVGW0 for partially self-consistent results at moderate cost
• For large systems, use practical GW guide for convergence strategies
• Ensure k-point mesh is sufficiently dense for band gap convergence

Verification & Sources

Primary sources:

1. VASP GW practical guide: https://www.vasp.at/wiki/Practical_guide_to_GW_calculations
2. M. Shishkin and G. Kresse, Phys. Rev. B 75, 235102 (2007)
3. F. Fuchs et al., Phys. Rev. B 76, 115109 (2007)

Confidence: VERIFIED - Official VASP documentation and extensive literature