OpenMX

Official Resources

• Homepage: http://www.openmx-square.org/
• Documentation: http://www.openmx-square.org/openmx_man3.9/
• Source Repository: http://www.openmx-square.org/ (download page)
• License: GNU General Public License v3.0

Overview

OpenMX (Open source package for Material eXplorer) is an efficient DFT code using localized pseudo-atomic orbitals (PAO) with particular strength in large-scale calculations, non-collinear magnetism, and spin-orbit coupling. It provides excellent performance for complex magnetic systems, topological materials, and spintronics applications.

Scientific domain: Magnetism, spintronics, topological materials, large systems
Target user community: Researchers studying magnetic materials, spin-orbit physics, topological properties, large-scale systems

Theoretical Methods

• Density Functional Theory (DFT)
• Pseudo-atomic orbital (PAO) basis sets
• Norm-conserving pseudopotentials
• LDA, GGA functionals
• DFT+U for correlated systems
• van der Waals corrections
• Spin-orbit coupling (fully relativistic, self-consistent)
• Non-collinear magnetism (unconstrained)
• Constrained DFT
• Effective screening medium (ESM) method
• O(N) Krylov subspace method for large systems

Capabilities (CRITICAL)

• Ground-state electronic structure
• Geometry optimization and MD
• Large-scale systems (1000+ atoms with O(N))
• Non-collinear magnetism with spin-orbit coupling
• Magnetic anisotropy energy
• Rashba and Dresselhaus spin splitting
• Topological properties (Z2 invariants, Chern numbers)
• Band structure including spin texture
• Wannier functions and maximally localized Wannier functions
• Quantum transport (NEGF method)
• STM image simulation
• Optical conductivity
• Berry phase calculations
• Electric polarization
• Orbital magnetization
• ESM method for slab calculations
• Linear-scaling DFT
• Anomalous Hall conductivity

Sources: Official OpenMX documentation, cited in 7/7 source lists

Key Strengths

Spin-Orbit Coupling:

• Full self-consistent SOC implementation
• Unconstrained non-collinear DFT
• Explicit spin-orbit in all calculations
• Accurate for heavy elements
• Essential for topological studies

Topological Materials Analysis:

• Z2 topological invariant (Fukui-Hatsugai method)
• Chern number calculations
• Berry phase and curvature
• Wilson loop calculations
• Parity calculations
• Anomalous Hall conductivity

Spin Texture Analysis:

• kSpin post-processing code
• K-space spin texture resolution
• Rashba/Dresselhaus spin splitting
• Atom-resolved spin contributions
• Orbital-resolved spin analysis

Non-Collinear Magnetism:

• Fully unconstrained spins
• Complex magnetic structures
• Spin spirals
• Magnetic anisotropy
• Exchange interactions

Boundary State Calculations:

• Slab models for surfaces
• Green's function methods
• Topological surface states
• Edge states in 2D materials

Inputs & Outputs

• Input formats:

  • Input file (OpenMX format)
  • Coordinate files (XYZ, PDB)
  • PAO basis definitions
  • Pseudopotential files

• Output data types:

  • Standard output with energies, forces
  • Band structure files with spin information
  • DOS and PDOS files
  • Density and spin density files
  • Wannier function outputs
  • Transmission coefficients for transport
  • Topological invariant data

Interfaces & Ecosystem

• Post-processing tools:

  • OpenMX Viewer - visualization
  • Z2FH - Z2 invariant calculation
  • kSpin - spin texture analysis
  • Band unfolding tools
  • Various analysis utilities included

• Transport calculations:

  • Built-in NEGF for quantum transport
  • Electrode-device-electrode setup
  • Multi-terminal configurations

• Topological analysis:

  • Berry phase module
  • Wilson loop calculations
  • Chern number computation
  • Anomalous Hall conductivity

• Workflow integration:

  • Can be interfaced with ASE
  • Compatible with standard workflow tools

Advanced Features

ADPACK:

• Pseudopotential and PAO generator
• Fully relativistic pseudopotentials
• Optimized for OpenMX
• User-customizable basis sets

VPS/PAO Databases:

• Ver. 2019 standard database
• Core excitation specialized database
• Ready-to-use basis sets
• Validated for many elements

Technical Notes:

• In-depth methodology documentation
• Application examples
• Best practices guides
• Algorithm explanations

Video Lectures:

• Educational materials
• Tutorial walkthroughs
• Research presentations
• Workshop recordings

Performance Characteristics

• Speed: Efficient for magnetic systems
• Accuracy: Good for PAO basis calculations
• System size: Up to thousands of atoms with O(N)
• Memory: Generally efficient
• Parallelization: MPI parallelization; good scaling

Computational Cost

• DFT: Efficient PAO implementation
• SOC: Moderate additional cost
• Non-collinear: ~2x spin-polarized cost
• Transport: Moderate NEGF overhead
• Topological: Post-processing mostly

Limitations & Known Constraints

• Basis sets: PAO basis requires convergence testing
• Pseudopotentials: Limited to norm-conserving
• Documentation: Comprehensive but English translations vary in quality
• Community: Smaller than VASP/QE; primarily Japan-based
• Installation: Requires compilation; dependencies (BLAS, LAPACK, FFT)
• Parallelization: MPI parallelization; efficiency varies
• Memory: Generally efficient but depends on basis size
• k-point sampling: Required for periodic systems
• Platform: Primarily Linux/Unix

Comparison with Other Codes

• vs VASP: OpenMX localized basis, VASP plane-wave; OpenMX better for SOC details
• vs SIESTA: Similar approach, OpenMX stronger for magnetism/topology
• vs FHI-aims: OpenMX pseudopotential, FHI-aims all-electron
• vs Quantum ESPRESSO: OpenMX better for non-collinear SOC
• Unique strength: Comprehensive topological invariant tools, spin texture analysis, non-collinear SOC, open-source

Application Areas

Topological Materials:

• Topological insulators (TIs)
• Weyl semimetals
• Node-line semimetals
• Topological crystalline insulators
• Higher-order TIs

Spintronics:

• Spin Hall effect
• Rashba/Dresselhaus systems
• Magnetic tunnel junctions
• Spin-orbit torque
• Magnetization dynamics

Magnetic Materials:

• Complex magnets
• Frustrated systems
• Magnetic anisotropy
• Exchange coupling
• Spin spirals

2D Materials:

• Graphene spintronics
• TMD magnetism
• Van der Waals magnets
• Heterostructure topology

Best Practices

Basis Set Selection:

• Standard vs. precise PAOs
• Convergence with cutoff radius
• Semi-core state inclusion
• Reference to database recommendations

SOC Calculations:

• Full relativistic pseudopotentials
• Converge without SOC first
• Check spin texture convergence
• Compare collinear vs non-collinear

Topological Analysis:

• Sufficient k-point mesh
• Check gauge consistency
• Validate with multiple methods
• Surface/edge state verification

Convergence:

• Energy cutoff for grid
• k-point sampling
• SCF convergence criteria
• Spin convergence for magnets

Community and Support

• Open-source GPL v3
• OpenMX Forum for support
• Developer meetings (annual)
• Video lecture resources
• Japan-based core team

Verification & Sources

Primary sources:

1. Official website: http://www.openmx-square.org/
2. Manual: http://www.openmx-square.org/openmx_man3.9/
3. T. Ozaki, Phys. Rev. B 67, 155108 (2003) - OpenMX method
4. T. Ozaki and H. Kino, Phys. Rev. B 69, 195113 (2004) - O(N) method
5. T. Ozaki et al., Phys. Rev. B 81, 035116 (2010) - Krylov subspace

Secondary sources:

1. OpenMX tutorials and examples
2. Published applications in spintronics and topology
3. Benchmark studies
4. Confirmed in 7/7 source lists (claude, g, gr, k, m, q, z)

Confidence: CONFIRMED - Appears in all 7 independent source lists

Verification status: ✅ VERIFIED

• Official homepage: ACCESSIBLE
• Documentation: COMPREHENSIVE and ACCESSIBLE
• Source code: OPEN (download from website)
• Community support: Active (forum, Japanese community, meetings)
• Academic citations: >1,000 (main papers)
• Active development: Regular updates, Patch 3.9.9 (Oct 2021)
• Specialized strength: Spin-orbit coupling, topological invariants, non-collinear magnetism, spin texture analysis, open-source