chem-sorption-gcmc

Goal

To predict the macroscopic adsorption uptake of a gas (or gas mixture) in a porous material at a specific temperature and pressure. The skill relies on Grand Canonical Monte Carlo (GCMC) simulations where the host-guest and guest-guest interactions are calculated using a Machine Learning Interatomic Potential (MLIP: MACE, FairChem, MatGL).

Prerequisites

• Input: A relaxed framework structure in CIF (or XYZ) format. The structure should ideally be processed by chem-sorption-relax to ensure proper supercell dimensions.
• Conda environment: Depends on the MLIP used (e.g., fairchem-agent, mace-agent, matgl-agent).

Instructions

1. Perform Single-Component GCMC (Optional): If you are investigating a single gas species, use run_gcmc.py.

# Env: fairchem-agent (or other MLIP-specific env)
python .agents/skills/chem-sorption-gcmc/scripts/run_gcmc.py \
    --cif path/to/relaxed_supercell.cif \
    --calculator fairchem \
    --model-name uma-s-1p1 \
    --task-name omol \
    --steps 50000 \
    --temperature-K 298 \
    --pressure-bar 1.0 \
    --adsorbate CO2 \
    --output-dir ./results/single_gcmc

2. Perform Multi-Component GCMC (Optional): If you are simulating a gas mixture (e.g. flue gas separation 15% CO2 / 85% N2), use run_gcmc_multi.py.

# Env: fairchem-agent
python .agents/skills/chem-sorption-gcmc/scripts/run_gcmc_multi.py \
    --cif path/to/relaxed_supercell.cif \
    --calculator fairchem \
    --model-name uma-s-1p1 \
    --task-name omol \
    --steps 50000 \
    --temperature-K 298 \
    --gases CO2 N2 \
    --y 0.15 0.85 \
    --p-total-bar 1.0 \
    --output-dir ./results/multi_gcmc

Key Parameters

• --cif: Path to the relaxed host framework.
• --calculator: The backend MLIP (fairchem, mace, matgl).
• --model-name: Name or path to the MLIP weights (e.g., uma-s-1p1.pt, MACE-MH-1).
• --task-name: Optional, required by some models (omol for UMA and MACE-MH).
• --steps: Number of Monte Carlo steps (minimum 50,000 recommended for equilibration).
• --temperature-K: Sim temperature.
• --pressure-bar (Single): Gas pressure in bar.
• --p-total-bar (Multi): Total mixture pressure in bar.
• --gases / --y (Multi): Species list and corresponding mole fractions in the vapor phase.

Examples

Example 1: Generating an Isotherm Point (CO2, 0.1 bar, 298K) with UMA:

# Env: fairchem-agent
python .agents/skills/chem-sorption-gcmc/scripts/run_gcmc.py \
    --cif ./data/MOF-5_supercell.cif \
    --calculator fairchem \
    --model-name uma-s-1p1 \
    --task-name omol \
    --steps 50000 \
    --temperature-K 298 \
    --pressure-bar 0.1 \
    --adsorbate CO2 \
    --output-dir ./out/0.1_bar

Constraints

• Simulation Time: GCMC with MLIPs can be computationally intensive. Use GPUs when available (--device cuda).
• Equilibration: You MUST check the generated nmols.png and energy.png inside the output-dir to visually confirm that the number of molecules and energy have plateaued (equilibrated). If the trend is still rising/falling at the end of the simulation, you must re-run with more --steps (or restart the trajectory).
• Restarting: You can pass --restart-traj ./out/mc.traj to continue a previous run.

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Author: Artur Lyssenko Contact: GitHub @arturlyssenko12