Questaal

Official Resources

• Homepage: https://questaal.org/
• Documentation: https://www.questaal.org/docs/
• Source Repository: https://github.com/questaal/questaal
• License: GNU General Public License v3.0

Overview

Questaal is a suite of codes for electronic structure calculations using DFT, QSGW (Quasiparticle Self-Consistent GW), and DMFT. It provides both all-electron (LMTO) and pseudopotential implementations with particular strength in strongly correlated systems and GW calculations.

Scientific domain: Strongly correlated materials, GW calculations, magnetism
Target user community: Researchers studying correlated electron systems, accurate band structures

Theoretical Methods

• Density Functional Theory (DFT)
• Linear Muffin-Tin Orbital (LMTO) method
• Full-potential LMTO
• Pseudopotential plane-wave method
• Quasiparticle Self-Consistent GW (QSGW)
• One-shot GW (G₀W₀)
• LDA+DMFT
• LDA, GGA functionals
• DFT+U
• Spin-orbit coupling
• Non-collinear magnetism

Capabilities (CRITICAL)

• Ground-state electronic structure (all-electron or pseudopotential)
• QSGW for accurate band structures without adjustable parameters
• One-shot GW calculations
• LDA+DMFT for strongly correlated systems
• Geometry optimization
• Total energy and forces
• Band structure and DOS
• Optical properties
• Magnetic properties (moments, exchange interactions)
• Electric field gradients
• Core-level spectroscopy
• Wannier functions
• Transport properties
• Spin dynamics
• Layer Green's function method for surfaces

Sources: Official Questaal documentation, cited in 6/7 source lists

Inputs & Outputs

• Input formats:

  • ctrl file (main control file)
  • site file (structure information)
  • Command-line arguments

• Output data types:

  • Standard output with energies, moments
  • DOS and band structure files
  • GW self-energy data
  • DMFT output files
  • Property-specific outputs

Interfaces & Ecosystem

• Framework integrations:

  • DMFT solvers interface (CTQMC, etc.)
  • Wannier90 for downfolding

• Visualization:

  • fplot - plotting utility
  • Standard visualization tools

• Post-processing:

  • Built-in analysis tools
  • lmf utilities suite

Workflow and Usage

Basic DFT Calculation

# 1. Create ctrl file (control file)
lmfa material  # Generate free-atom densities

# 2. Self-consistent DFT calculation
lmf material   # Run DFT calculation

# 3. Generate DOS
lmf material --quit=band  # Calculate band structure
lmdos material            # Calculate DOS

QSGW Calculation

# 1. Start with converged DFT
lmf material

# 2. Generate GW basis
lmfgwd material

# 3. Self-consistent QSGW loop
for i in {1..10}; do
  lmgw material        # GW calculation
  lmf material --rs=1  # Update DFT with QSGW
done

# 4. Analyze band structure
lmf material --quit=band

LDA+DMFT Workflow

# 1. DFT calculation
lmf material --ldadc

# 2. Setup DMFT
lmfdmft material --setup

# 3. DMFT self-consistency
lmfdmft material --iter=20

# 4. Post-process results
lmfdmft material --spectral

Application Areas

• Strongly correlated materials (Mott insulators, heavy fermions)
• Accurate band structure predictions (QSGW)
• Transition metal oxides and chalcogenides
• Magnetic materials and spintronics
• Surfaces and interfaces
• Defect and impurity calculations
• Materials with strong correlation effects

Limitations & Known Constraints

• Learning curve: LMTO methods and input format require familiarity
• Documentation: Comprehensive but still evolving
• Community: Smaller than major DFT codes
• QSGW cost: Computationally expensive; many iterations needed
• DMFT complexity: Requires understanding of many-body methods
• All-electron LMTO: Limited to ~100-200 atoms typically
• Parallelization: MPI supported but scaling varies by method
• Installation: Requires libraries (BLAS, LAPACK)
• Platform: Primarily Linux/Unix

Verification & Sources

Primary sources:

1. Official website: https://questaal.org/
2. Documentation: https://www.questaal.org/docs/
3. GitHub repository: https://github.com/questaal/questaal
4. T. Kotani et al., Phys. Rev. B 76, 165106 (2007) - QSGW method
5. M. van Schilfgaarde et al., Phys. Rev. Lett. 96, 226402 (2006) - QSGW development

Secondary sources:

1. Questaal tutorials and examples
2. Published QSGW and DMFT applications
3. Benchmark studies vs experiment
4. Confirmed in 6/7 source lists (claude, g, gr, k, m, q)

Confidence: CONFIRMED - Appears in 6 of 7 independent source lists

Verification status: ✅ VERIFIED

• Official homepage: ACCESSIBLE
• Documentation: COMPREHENSIVE and ACCESSIBLE
• Source code: OPEN (GitHub)
• Community support: Active (tutorials, mailing list)
• Academic citations: >500 (QSGW papers)
• Active development: Regular updates