Official Resources
- Homepage: https://salmon-tddft.jp/
- Documentation: https://salmon-tddft.jp/wiki/
- Source Repository: https://github.com/SALMON-TDDFT/SALMON2
- License: Apache License 2.0
Overview
SALMON (Scalable Ab-initio Light-Matter simulator for Optics and Nanoscience) is a massively-parallel software for ab-initio quantum-mechanical calculations of electron dynamics and light-matter interactions. It is based on time-dependent density functional theory (TDDFT) and specializes in simulating ultrafast phenomena, nonlinear optical responses, and strong-field physics in periodic systems.
Scientific domain: Ultrafast electron dynamics, strong-field physics, nonlinear optics, photonics
Target user community: Researchers studying light-matter interaction, ultrafast processes, high-harmonic generation
Theoretical Methods
- Time-Dependent Density Functional Theory (TDDFT)
- Real-time TDDFT propagation
- Density Functional Theory (DFT) for ground state
- Local Density Approximation (LDA)
- Generalized Gradient Approximation (GGA)
- Plane-wave basis with pseudopotentials
- Real-space grid representation
- Finite-difference time-domain (FDTD) for Maxwell equations
- Coupled Maxwell-TDDFT calculations
- Adiabatic local density approximation (ALDA)
- Time-dependent current-density functional theory (TDCDFT)
Capabilities (CRITICAL)
- Ground-state DFT calculations for periodic systems
- Real-time TDDFT electron dynamics
- Light-matter interaction in strong laser fields
- Linear and nonlinear optical response
- High-harmonic generation (HHG)
- Ultrafast photoexcitation dynamics
- Attosecond pulse generation simulation
- Photoelectron momentum distributions
- Time-resolved absorption spectra
- Dielectric functions (frequency-dependent)
- Second and third harmonic generation
- Multi-scale Maxwell-TDDFT coupling
- Propagation in bulk and nanostructures
- Isolated molecules and periodic solids
- Massively parallel (10,000+ CPU cores)
- GPU acceleration (CUDA)
- Electromagnetic field propagation
Sources: Official SALMON documentation (https://salmon-tddft.jp/), cited in 6/7 source lists
Key Features and Strengths
Scalability:
- Designed for modern massively parallel supercomputers
- Excellent scaling to 10,000+ cores demonstrated
- Hybrid MPI+OpenMP parallelization
- GPU acceleration for key kernels
- Optimized for K computer, Fugaku, and similar HPC systems
Multi-scale Capabilities:
- Coupled quantum-classical (Maxwell-TDDFT)
- Seamless integration of ab initio and classical electromagnetism
- Propagation effects in extended systems
- Near-field to far-field transformations
Strong-Field Physics:
- Arbitrary laser pulse shapes and polarizations
- Multiple laser pulses
- Spatially non-uniform fields
- Tunneling ionization and above-threshold ionization
- Strong-field approximation benchmarking
Inputs & Outputs
-
Input formats:
- Namelist-based input file (salmon.inp)
- XYZ format for atomic coordinates
- CIF format support
- Pseudopotential files (various formats)
- Laser pulse specification files
-
Output data types:
- Time-dependent electron density
- Induced current density
- Photoelectron spectra
- High-harmonic spectra
- Time-resolved observables
- Absorption cross sections
- Dielectric functions
- Maxwell field distributions
- Energy flow (Poynting vector)
Interfaces & Ecosystem
Workflow and Usage
Typical Workflow:
- Ground state: Compute DFT ground state
- Pulse definition: Define laser pulse parameters
- RT-TDDFT: Propagate in real time under laser field
- Analysis: Extract observables (HHG, photoelectron, etc.)
- Post-process: Analyze spectra and dynamics
Example Applications:
- HHG in solids: High-harmonic generation in semiconductors
- Attosecond physics: Attosecond pulse characterization
- Plasmonics: Light-matter interaction in nanostructures
- Ultrafast dynamics: Carrier dynamics in excited materials
- Nonlinear optics: SHG/THG in crystals
Advanced Features
Maxwell-TDDFT Coupling:
- Self-consistent coupling of quantum and classical
- Light propagation through quantum systems
- Near-field enhancement effects
- Collective plasmonic responses
Multi-photon Processes:
- Above-threshold ionization
- Multi-photon absorption
- Strong-field tunneling
- Plateau and cutoff structures in HHG
Periodic and Finite Systems:
- Bulk crystals with periodic boundary conditions
- Surfaces and slabs
- Isolated molecules (large simulation boxes)
- Nanostructures and clusters
Computational Efficiency
- Parallelization strategy: 3D domain decomposition + k-point parallelization
- Memory optimization: Distributed memory model
- GPU offload: Critical kernels GPU-accelerated
- I/O optimization: Parallel I/O for large-scale simulations
- Load balancing: Dynamic load balancing algorithms
Performance Benchmarks
- Demonstrated petascale performance
-
80% parallel efficiency on 10,000+ cores
- GPU acceleration provides 2-5x speedup
- Production runs on Fugaku supercomputer
Limitations & Known Constraints
- Pseudopotentials: Limited to norm-conserving; no PAW
- Exchange-correlation: ALDA approximation; no memory effects
- System size: RT-TDDFT expensive; typically <1000 atoms
- Time step: Small time steps required for real-time propagation
- Memory: Large-scale simulations memory-intensive
- Learning curve: Steep; requires TDDFT and strong-field knowledge
- Documentation: Good but technical; assumes familiarity with ultrafast physics
- Platform: Primarily Linux/Unix; HPC focus
- Compilation: Requires careful build for optimal performance
- Input format: Namelist-based; requires understanding of parameters
Comparison with Other Codes
- vs Octopus: SALMON better scaling, optimized for HPC
- vs Quantum ESPRESSO TDDFT: SALMON more specialized for strong fields
- vs GPAW: SALMON has Maxwell coupling, better for photonics
- Unique strength: Multi-scale Maxwell-TDDFT, petascale performance
Application Areas
Strong-Field Physics:
- High-harmonic generation in solids and molecules
- Attosecond pulse generation and characterization
- Strong-field ionization dynamics
Photonics and Plasmonics:
- Light propagation in nanostructures
- Plasmonic enhancement effects
- Near-field to far-field coupling
Ultrafast Science:
- Pump-probe spectroscopy simulations
- Carrier dynamics in excited states
- Transient absorption spectroscopy
Materials Science:
- Optical properties of materials
- Nonlinear optical coefficients
- Dielectric response functions
Verification & Sources
Primary sources:
- Official website: https://salmon-tddft.jp/
- Documentation: https://salmon-tddft.jp/wiki/
- GitHub repository: https://github.com/SALMON-TDDFT/SALMON2
- M. Noda et al., Comput. Phys. Commun. 235, 356 (2019) - SALMON paper
- K. Yabana et al., Phys. Rev. B 85, 045134 (2012) - RT-TDDFT method
- SALMON user manual and tutorials
Secondary sources:
- SALMON workshops and schools
- Published HHG and ultrafast dynamics studies
- Fugaku supercomputer application showcase
- 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, Apache License 2.0)
- Community support: Active (mailing list, GitHub issues)
- Academic citations: >100 (method and code papers)
- Active development: Regular releases, Fugaku optimization
- Benchmark validation: Extensive HHG comparisons with experiments
- Supercomputer partnerships: K computer, Fugaku flagship applications