IRC Verification with Sella

Verify that a saddle-point-optimized TS connects the intended reactant and product.

Scope

• Domain: molecular chemistry only (non-periodic systems).
• Trigger: user has optimized reactant/product + optimized TS and needs IRC endpoint verification.
• Exclusions: periodic systems and barrier-only workflows.

Tool

verify_irc_sella.py

Runs forward/reverse IRC from the TS, optionally relaxes endpoints, then checks mapping quality.

Use with MACE

# Env: mace-agent
python .agents/skills/chem-irc-verification/scripts/verify_irc_sella.py \
  --reactant reactant_optimized.xyz \
  --product product_optimized.xyz \
  --ts ts_optimized.xyz \
  --model_type mace \
  --model_name MACE-OFF23-small \
  --fmax 0.02 \
  --steps 1000 \
  --rmsd_threshold 0.20 \
  --relax_endpoints true \
  --endpoint_relax_fmax 0.02 \
  --output_dir results/irc

Use with FAIRChem (UMA)

# Env: fairchem-agent
python .agents/skills/chem-irc-verification/scripts/verify_irc_sella.py \
  --reactant reactant_optimized.xyz \
  --product product_optimized.xyz \
  --ts ts_optimized.xyz \
  --model_type fairchem \
  --model_name uma-s-1p1 \
  --task_name omol \
  --fmax 0.02 \
  --steps 1000 \
  --rmsd_threshold 0.20 \
  --relax_endpoints true \
  --endpoint_relax_fmax 0.02 \
  --output_dir results/irc

Arguments

• --reactant: required optimized reactant geometry.
• --product: required optimized product geometry.
• --ts: required saddle-point-optimized TS geometry.
• --model_type: required backend (mace or fairchem).
• --model_name: optional model identifier/checkpoint.
• --task_name: optional model head/task (for UMA molecular runs use omol).
• --device: auto|cpu|cuda (default auto).
• --fmax: IRC convergence threshold in eV/A (default 0.02).
• --steps: maximum IRC steps per direction (default 1000).
• --rmsd_threshold: endpoint RMSD threshold in A (default 0.20).
• --relax_endpoints: true|false, relax IRC endpoints before matching (default true).
• --endpoint_relax_fmax: force threshold for optional endpoint relaxation (default 0.02).
• --output_dir: required output directory.

Outputs

• irc_forward.traj, irc_reverse.traj: IRC trajectories.
• irc_forward.log, irc_reverse.log: IRC logs.
• irc_forward_endpoint.xyz, irc_reverse_endpoint.xyz: terminal endpoint geometries.
• irc_verification_results.json: endpoint assignment and pass/fail summary.

irc_verification_results.json fields include:

• selected endpoint assignment (endpoint_mapping)
• per-pair metrics (connectivity_match, rmsd_angstrom, thresholds)
• all candidate assignments with total RMSD
• final decision (verification_passed)

Verification Criterion

Verification passes only if both mapped endpoint-target pairs satisfy:

• same formula and atom order
• connectivity graph match
• Kabsch-aligned RMSD <= rmsd_threshold

Default criterion: both pairs must pass with rmsd_threshold = 0.20 A.

Model Guidance

• Recommended for molecules:
  • MACE-OFF23-small / MACE-OFF23-medium
  • uma-s-1p1 with --task_name omol
• Use the same backend/model/head as TS optimization to avoid model inconsistency.

Prerequisites And Constraints

• Activate mace-agent or fairchem-agent depending on backend.
• Script enforces pbc=False for all inputs.
• Reactant/product/TS must have identical composition and consistent atom ordering.

Examples

See examples/ directory for sample inputs and outputs.

Author: Juno Nam Contact: GitHub @recisic