name: fairchem description: Expert guidance for Meta's FAIRChem library - machine learning methods for materials science and quantum chemistry using pretrained UMA models with ASE integration for fast, accurate predictions

FAIRChem Skill

This skill provides expert guidance for using FAIRChem (formerly OCP - Open Catalyst Project), Meta's FAIR Chemistry library of machine learning methods for materials science and quantum chemistry.

When to Use This Skill

Use this skill when:

• Using ML potentials for materials and molecular simulations
• Running fast geometry optimizations with pretrained models
• Performing large-scale MD simulations
• Calculating energies and forces without DFT
• Working with the UMA (Universal Materials Algebra) models
• Needing predictions for catalysis, molecules, crystals, or MOFs
• Integrating ML models with ASE workflows
• Scaling calculations across multiple GPUs

What is FAIRChem?

FAIRChem is Meta's machine learning framework for chemistry that provides:

• Pretrained UMA models (uma-s-1p1, uma-m-1p1) for universal predictions
• Domain-specific tasks: catalysis (oc20), materials (omat), molecules (omol), MOFs (odac), crystals (omc)
• ASE integration via FAIRChemCalculator
• Multi-GPU support for distributed inference
• Fast predictions: 100-1000× faster than DFT

Key Advantage

FAIRChem allows you to use the same model across different chemistry domains by simply changing the task_name parameter.

Core Concepts

1. UMA Models

Universal Materials Algebra models trained on diverse datasets:

• uma-s-1p1: Small model (~50M parameters) - faster inference
• uma-m-1p1: Medium model (~300M parameters) - higher accuracy

2. Task Names (Domains)

Specify the chemistry domain for domain-specific predictions:

• oc20: Catalysis (surfaces with adsorbates)
• omat: Inorganic materials (crystals, bulk)
• omol: Molecules (organic chemistry)
• odac: Metal-organic frameworks (MOFs)
• omc: Molecular crystals

3. FAIRChemCalculator

ASE calculator interface that wraps UMA models:

• Drop-in replacement for DFT calculators
• Supports all ASE workflows
• Provides energies, forces, and stresses
• Compatible with optimization, MD, NEB

4. Inference Settings

Performance optimization modes:

• turbo: Maximum speed, slightly reduced accuracy
• Standard: Balanced speed and accuracy
• Multi-GPU: Distributed inference with workers=N

Installation

# Install fairchem
pip install fairchem-core

# For GPU support
pip install fairchem-core[gpu]

# Hugging Face login (required for UMA models)
pip install huggingface-hub
huggingface-cli login

Note: You must have a Hugging Face account and request access to the UMA model repository.

Basic Usage Pattern

Standard Workflow

from fairchem.data.ase import FAIRChemCalculator
from fairchem.predict import load_predict_unit
from ase.build import bulk
from ase.optimize import LBFGS

# 1. Load pretrained model
predict_unit = load_predict_unit("uma-m-1p1")

# 2. Create calculator for specific domain
calc = FAIRChemCalculator(
    predict_unit=predict_unit,
    task_name="omat"  # Choose domain
)

# 3. Use with ASE
atoms = bulk("Cu", "fcc", a=3.6)
atoms.calc = calc

# 4. Calculate properties
energy = atoms.get_potential_energy()
forces = atoms.get_forces()

# 5. Optimize structure
opt = LBFGS(atoms)
opt.run(fmax=0.05)

Common Workflows

Workflow 1: Catalysis - Surface Adsorption

from fairchem.data.ase import FAIRChemCalculator
from fairchem.predict import load_predict_unit
from ase.build import fcc111, add_adsorbate
from ase.optimize import LBFGS
from ase.constraints import FixAtoms

# Load model
predict_unit = load_predict_unit("uma-m-1p1")

# Create calculator for catalysis
calc = FAIRChemCalculator(
    predict_unit=predict_unit,
    task_name="oc20"  # Catalysis domain
)

# Build slab with adsorbate
slab = fcc111("Cu", size=(4, 4, 4), vacuum=10.0)
add_adsorbate(slab, "CO", height=2.0, position="fcc")

# Fix bottom layers
n_atoms_per_layer = 16
constraint = FixAtoms(indices=range(n_atoms_per_layer * 2))
slab.set_constraint(constraint)

# Attach calculator and optimize
slab.calc = calc
opt = LBFGS(slab, trajectory="slab_opt.traj")
opt.run(fmax=0.05)

# Get results
E = slab.get_potential_energy()
forces = slab.get_forces()

Workflow 2: Bulk Materials - Lattice Optimization

from fairchem.data.ase import FAIRChemCalculator
from fairchem.predict import load_predict_unit
from ase.build import bulk
from ase.optimize import FIRE
from ase.filters import FrechetCellFilter

# Load model
predict_unit = load_predict_unit("uma-m-1p1")

# Calculator for materials
calc = FAIRChemCalculator(
    predict_unit=predict_unit,
    task_name="omat"  # Materials domain
)

# Create bulk structure
atoms = bulk("Fe", "bcc", a=2.87)
atoms.calc = calc

# Optimize both positions and cell
# FrechetCellFilter allows cell parameters to change
ucf = FrechetCellFilter(atoms)
opt = FIRE(ucf)
opt.run(fmax=0.05)

# Results
optimized_lattice = atoms.cell.cellpar()[0]
print(f"Optimized lattice constant: {optimized_lattice:.3f} Å")

Workflow 3: Molecular Dynamics

from fairchem.data.ase import FAIRChemCalculator
from fairchem.predict import load_predict_unit
from ase.build import bulk
from ase.md.velocitydistribution import MaxwellBoltzmannDistribution
from ase.md.langevin import Langevin
from ase import units

# Load with turbo settings for speed
predict_unit = load_predict_unit(
    "uma-s-1p1",  # Use small model for MD
    inference_settings="turbo"
)

# Calculator for MD
calc = FAIRChemCalculator(
    predict_unit=predict_unit,
    task_name="omat",
    workers=4  # Multi-GPU for large systems
)

# Large system
atoms = bulk("C", "fcc", a=3.57) * (20, 20, 20)  # 8000 atoms
atoms.calc = calc

# Initialize velocities
MaxwellBoltzmannDistribution(atoms, temperature_K=300)

# Run NVT dynamics
dyn = Langevin(
    atoms,
    timestep=1.0 * units.fs,
    temperature_K=300,
    friction=0.002
)

# Run
from ase.io.trajectory import Trajectory
traj = Trajectory("md.traj", "w", atoms)
dyn.attach(traj.write, interval=10)
dyn.run(5000)

Workflow 4: Molecular Systems

from fairchem.data.ase import FAIRChemCalculator
from fairchem.predict import load_predict_unit
from ase.build import molecule
from ase.optimize import LBFGS

# Load model
predict_unit = load_predict_unit("uma-m-1p1")

# Calculator for molecules
calc = FAIRChemCalculator(
    predict_unit=predict_unit,
    task_name="omol"  # Molecular domain
)

# Build molecule
mol = molecule("H2O")
mol.center(vacuum=10.0)
mol.calc = calc

# Optimize
opt = LBFGS(mol, trajectory="mol_opt.traj")
opt.run(fmax=0.05)

# Get properties
E = mol.get_potential_energy()
forces = mol.get_forces()

Workflow 5: NEB Calculations

from fairchem.data.ase import FAIRChemCalculator
from fairchem.predict import load_predict_unit
from ase.neb import NEB
from ase.optimize import BFGS
from ase.io import read

# Load model
predict_unit = load_predict_unit("uma-m-1p1")

# Calculator
calc = FAIRChemCalculator(
    predict_unit=predict_unit,
    task_name="oc20"
)

# Load initial and final states
initial = read("initial.traj")
final = read("final.traj")

# Create NEB
images = [initial]
images += [initial.copy() for i in range(5)]
images += [final]

neb = NEB(images)
neb.interpolate()

# Attach calculator to intermediate images
for image in images[1:-1]:
    image.calc = calc

# Optimize
opt = BFGS(neb, trajectory="neb.traj")
opt.run(fmax=0.05)

# Analyze
energies = [img.get_potential_energy() for img in images]
barrier = max(energies) - energies[0]
print(f"Barrier: {barrier:.3f} eV")

Model Loading Options

Load Pretrained UMA Model

from fairchem.predict import load_predict_unit

# Standard loading
predict_unit = load_predict_unit("uma-m-1p1")

# With turbo mode (faster, slight accuracy trade-off)
predict_unit = load_predict_unit(
    "uma-m-1p1",
    inference_settings="turbo"
)

# Specify device
predict_unit = load_predict_unit(
    "uma-m-1p1",
    device="cuda:0"
)

# Load local checkpoint
predict_unit = load_predict_unit(
    "/path/to/checkpoint.pt",
    device="cuda"
)

Available Models

• uma-s-1p1: Small, fast (~50M params)
• uma-m-1p1: Medium, accurate (~300M params)

Task Selection Guide

Performance Optimization

Multi-GPU Inference

# Use multiple GPUs automatically
calc = FAIRChemCalculator(
    predict_unit=predict_unit,
    task_name="omat",
    workers=8  # Use 8 GPUs
)

# Achieves ~10× speedup on 8× H100 GPUs

Turbo Mode

# Trade slight accuracy for speed
predict_unit = load_predict_unit(
    "uma-s-1p1",  # Small model
    inference_settings="turbo"
)

# Good for:
# - MD simulations
# - Large systems
# - Initial screening

Batch Predictions

# For multiple similar calculations
from fairchem.data.ase import batch_predict

structures = [atoms1, atoms2, atoms3, ...]

results = batch_predict(
    structures,
    predict_unit=predict_unit,
    task_name="omat"
)

Best Practices

1. Task Selection

Always choose the appropriate task for your system:

• Surfaces with adsorbates → oc20
• Bulk materials → omat
• Isolated molecules → omol
• MOFs → odac
• Molecular crystals → omc

2. Model Selection

• Initial screening: Use uma-s-1p1 + turbo
• Production calculations: Use uma-m-1p1
• Very large systems: Use uma-s-1p1 + workers

3. Validation

ML models have different error characteristics than DFT:

# Always validate critical results
# Compare ML prediction with DFT for representative cases
ml_energy = atoms.get_potential_energy()  # FAIRChem
atoms.calc = Vasp(...)  # Switch to DFT
dft_energy = atoms.get_potential_energy()
error = abs(ml_energy - dft_energy)

4. Uncertainty Quantification

FAIRChem models provide predictions but not uncertainty:

• Test on similar known systems first
• Validate against DFT for critical results
• Use ensemble of predictions if available

5. Memory Management

For large systems:

# Use turbo mode
predict_unit = load_predict_unit(
    "uma-s-1p1",
    inference_settings="turbo"
)

# Distribute across GPUs
calc = FAIRChemCalculator(
    predict_unit=predict_unit,
    task_name="omat",
    workers=4
)

Common Patterns

Energy Calculation

atoms.calc = calc
energy = atoms.get_potential_energy()  # eV
forces = atoms.get_forces()  # eV/Å
stress = atoms.get_stress()  # eV/ų

Geometry Optimization

from ase.optimize import LBFGS, FIRE, BFGS

# Fast convergence
opt = LBFGS(atoms, trajectory="opt.traj")
opt.run(fmax=0.05)

# For difficult systems
opt = FIRE(atoms)
opt.run(fmax=0.05)

Cell Optimization

from ase.filters import FrechetCellFilter

# Optimize both atoms and cell
ucf = FrechetCellFilter(atoms)
opt = FIRE(ucf)
opt.run(fmax=0.05)

Integration with ASE

FAIRChemCalculator is a full ASE calculator:

# All ASE functionality works
from ase.vibrations import Vibrations
from ase.thermochemistry import IdealGasThermo
from ase.eos import calculate_eos

# Vibrational analysis
vib = Vibrations(atoms)
vib.run()

# Thermochemistry
thermo = IdealGasThermo(...)

# Equation of state
eos = calculate_eos(atoms)

Troubleshooting

Hugging Face Authentication

# Login to Hugging Face
huggingface-cli login

# Request access to UMA models at:
# https://huggingface.co/meta-llama/uma-m-1p1

GPU Memory Issues

# Use smaller model
predict_unit = load_predict_unit("uma-s-1p1")

# Use turbo mode
predict_unit = load_predict_unit(
    "uma-s-1p1",
    inference_settings="turbo"
)

# Reduce batch size (if using batch predictions)

Slow Inference

# Enable turbo mode
inference_settings="turbo"

# Use multiple GPUs
workers=N

# Use smaller model
"uma-s-1p1"

Wrong Task Selection

# Symptoms: Poor predictions, unphysical results
# Solution: Verify task matches your system

# For surfaces + adsorbates:
task_name="oc20"  # NOT "omat" or "omol"

# For bulk materials:
task_name="omat"  # NOT "oc20"

Version Compatibility

Important: FAIRChem v2 is a breaking change from v1

• v2 code is NOT compatible with v1 models
• v1 code is NOT compatible with v2 models
• UMA models require FAIRChem >= 2.0

# Check version
import fairchem
print(fairchem.__version__)  # Should be >= 2.0 for UMA

Comparison with DFT

When to Use FAIRChem vs DFT

Use FAIRChem for:

• Initial screening of many structures
• Long MD simulations
• Large systems (>500 atoms)
• Rapid prototyping
• High-throughput workflows

Use DFT for:

• Final validation
• Novel chemistries outside training data
• When highest accuracy needed
• Electronic structure analysis
• Magnetic properties

Resources

When suggesting FAIRChem solutions:

• Specify correct task_name for the domain
• Recommend appropriate model (s vs m)
• Suggest performance optimizations (turbo, workers)
• Include validation against known results
• Mention Hugging Face authentication requirement
• Provide complete working examples
• Note v2 compatibility requirements

Example Response Pattern

When helping with FAIRChem:

1. Identify the chemistry domain (catalysis, materials, molecules, etc.)
2. Select appropriate task_name
3. Choose model based on accuracy/speed requirements
4. Provide complete code with imports
5. Suggest performance optimizations if needed
6. Recommend validation steps
7. Note any domain-specific considerations