ALM

Official Resources

• Homepage: https://github.com/ttadano/ALM (part of ALAMODE project)
• Documentation: https://alamode.readthedocs.io/en/latest/alm.html
• Source Repository: https://github.com/ttadano/alamode
• License: MIT License

Overview

ALM is the force constant extraction module of the ALAMODE software suite. It extracts harmonic and anharmonic interatomic force constants from first-principles displacement-force datasets using advanced fitting techniques including compressive sensing. ALM can extract 2nd, 3rd, 4th, and higher-order force constants efficiently, making it a key tool for setting up anharmonic lattice dynamics calculations.

Scientific domain: Force constant extraction, anharmonic lattice dynamics
Target user community: Researchers studying phonons and thermal transport

Theoretical Methods

• Least-squares fitting
• Compressive sensing (LASSO, elastic net)
• Symmetry constraints
• Cutoff-based cluster expansion
• Harmonic and anharmonic IFCs (2nd through 6th order)
• Regularization techniques
• Cross-validation

Capabilities (CRITICAL)

• Extract 2nd order (harmonic) force constants
• Extract 3rd, 4th, 5th, 6th order anharmonic force constants
• Compressive sensing for data efficiency
• Automatic symmetry implementation
• Compatible with any DFT code (via force-displacement data)
• Efficient algorithms for large systems
• Python and C++ interfaces
• Integration with ALAMODE for thermal conductivity

Sources: ALAMODE/ALM documentation, J. Phys.: Condens. Matter 26, 225402 (2014)

Key Strengths

• High-order IFCs: Up to 6th order anharmonicity
• Compressive sensing: Reduces required calculations
• Flexibility: Works with any DFT code
• Symmetry: Automatic symmetry constraints

Inputs & Outputs

• Input formats:

  • Displacement patterns
  • Forces from DFT calculations
  • Crystal structure
  • Symmetry information

• Output data types:

  • Harmonic force constants (phonopy format)
  • Anharmonic force constants (various orders)
  • ALAMODE format for thermal conductivity

Interfaces & Ecosystem

• ALAMODE: Core component for full thermal transport workflow
• phonopy: Export harmonic force constants
• DFT codes: Any code (via displacement-force data)
• Python/C++: Both interfaces available

Workflow and Usage

Extract Harmonic Force Constants:

# Generate displacements
alm -p input.in --suggest

# After DFT calculations
alm input.in

Extract Anharmonic (3rd order):

&general
  PREFIX = silicon
  MODE = optimize
  NAT = 8; NKD = 1
  KD = Si
/

&interaction
  NORDER = 2  # 2=3rd order
/

&optimize
  LMODEL = enet  # elastic net regression
/

Advanced Features

• Multiple regression methods (least-squares, LASSO, elastic net)
• Cross-validation for model selection
• Sparse optimization techniques
• High-order force constants for extreme anharmonicity

Performance Characteristics

• Fast fitting algorithms
• Handles large displacement datasets
• Efficient memory usage
• Parallelization support

Computational Cost

• DFT calculations: Dominant cost
• ALM fitting: Fast (seconds to minutes)
• Scales well with system size

Limitations & Known Constraints

• Requires DFT input: Not a DFT code itself
• Displacement generation: Manual or external tools
• Learning curve: Moderate
• High-order IFCs: Require many calculations

Comparison with Other Codes

• Part of ALAMODE: Integrated force constant extraction module
• vs hiPhive: Similar compressive sensing; ALM more established
• vs phono3py direct fit: ALM more flexible algorithms

Application Areas

• Anharmonic phonon calculations
• Thermal conductivity (via ALAMODE)
• Force constant database generation
• High-throughput phonon studies

Best Practices

• Use compressive sensing to reduce calculations
• Systematic convergence of cutoffs
• Cross-validation to prevent overfitting
• Test different regression methods

Community and Support

• Part of ALAMODE project (MIT license)
• GitHub repository
• ALAMODE documentation
• Active development
• User support via issues

Development

• Terumasa Tadano (Tohoku University)
• Part of ALAMODE development
• Regular updates
• Well-maintained

Research Impact

ALM provides efficient extraction of anharmonic force constants using advanced regression techniques, enabling accurate thermal transport calculations with reduced computational cost.

Verification & Sources

Primary sources:

1. GitHub: https://github.com/ttadano/alamode
2. Documentation: https://alamode.readthedocs.io/en/latest/alm.html
3. Publication: J. Phys.: Condens. Matter 26, 225402 (2014)

Confidence: VERIFIED - Part of ALAMODE

Verification status: ✅ VERIFIED

• Part of ALAMODE suite (MIT license)
• Documentation: COMPREHENSIVE
• Development: ACTIVE (Tohoku)
• Applications: Force constant extraction, compressive sensing, harmonic and anharmonic IFCs, integration with ALAMODE thermal transport