Tools · Fluids & Thermodynamics

RMG Mechanism Generator

Generate a detailed gas-phase kinetic mechanism from starting species, temperature, and pressure with the Reaction Mechanism Generator.

Updated October 1, 2026

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The Reaction Mechanism Generator (RMG-Py) builds a detailed kinetic mechanism automatically: starting from your species, it applies reaction families and estimated rate rules, adds the species and reactions that matter at your conditions, and stops when a termination criterion is met. Cantera runs mechanisms; this tool writes them. It runs on CPU and can take hours for larger systems.

Inputs

species: up to 20 starting species, each with a label, smiles, and mole_fraction; mark diluents such as N₂ or Ar "reactive": false. At least one must be reactive.
temperature_k and pressure_pa: the conditions of a constant-temperature, constant-pressure reactor.
termination: at least one of a reaction time (time_s), a conversion of one species ({"species": "CH4", "fraction": 0.9}), or a maximum number of species in the mechanism (max_num_species, up to 200).

RMG's default thermodynamic and kinetic libraries are used.

Outputs

File	Contents
`chem.yaml`	The mechanism in Cantera YAML
`chem.inp`	The mechanism in CHEMKIN format
`species_dictionary.txt`	Each species' structure (RMG adjacency lists)
`summary.json`	Run details and counts

Not covered

Temperature or pressure ranges, pressure-dependent networks, liquid-phase and solvent effects, your own seed mechanisms or libraries, and sensitivity analysis aren't available yet.

Generated mechanisms are often large: shrink one for your conditions with Mechanism Reduction, then simulate it in Cantera.

Run it from the API

Submit with Submit a job and the job_type below. Price it first with Estimate job reservation cost: submitting reserves that amount from your wallet, and the charge settles at the actual runtime.

RMG Mechanism Generator `rmg-mechanism`

Job type: rmg-mechanism
Hardware: cpu (default)
Typical runtime: 2 h on CPU

Payload

Payload fields
Field	Type	Description
`species[]`required	`species[]`	Limits: `min items 1, max items 20`
species.`label`required	`string`	Limits: `min length 1`
species.`smiles`required	`string`	Limits: `min length 1`
species.`mole_fraction`required	`number`	Limits: `> 0`
species.`reactive`	`boolean`
`temperature_k`required	`number`	Limits: `> 0`
`pressure_pa`required	`number`	Limits: `> 0`
`termination`required	`termination`
termination.`time_s`	`number`	Limits: `> 0`
termination.`conversion`	`object`
termination.conversion.`species`required	`string`	Limits: `min length 1`
termination.conversion.`fraction`required	`number`	Limits: `> 0, ≤ 1`
termination.`max_num_species`	`integer`	Limits: `≥ 1, ≤ 200`

Example

from cognichem_client import CogniChem

client = CogniChem.from_env()  # reads COGNICHEM_API_KEY
payload = {
    "species": [
        {
            "label": "CH4",
            "smiles": "C",
            "mole_fraction": 0.1,
            "reactive": True,
        },
        {
            "label": "O2",
            "smiles": "[O][O]",
            "mole_fraction": 0.2,
            "reactive": True,
        },
        {
            "label": "N2",
            "smiles": "N#N",
            "mole_fraction": 0.7,
            "reactive": False,
        },
    ],
    "temperature_k": 1350,
    "pressure_pa": 101325,
    "termination": {
        "time_s": 1,
        "conversion": {"species": "CH4", "fraction": 0.9},
        "max_num_species": 50,
    },
}

estimate = client.jobs.estimate(job_type="rmg-mechanism", payload=payload, resource="cpu")
print(f"Reserves ${estimate.cost:.2f}")

job = client.jobs.submit(
    job_name="my-rmg-mechanism-run",
    job_type="rmg-mechanism",
    payload=payload,
    resource="cpu",
)
status = client.jobs.wait(job.process_id)
if status.status == "completed":
    client.jobs.result(job.process_id, save_path=".")

curl -X POST "https://api.cognichem.com/api/v1/jobs/submit" \
  -H "X-Api-Key: $COGNICHEM_API_KEY" \
  -H "Idempotency-Key: $(uuidgen)" \
  -H "Content-Type: application/json" \
  -d '{
  "job_name": "my-rmg-mechanism-run",
  "job_type": "rmg-mechanism",
  "payload": {
    "species": [
      {
        "label": "CH4",
        "smiles": "C",
        "mole_fraction": 0.1,
        "reactive": true
      },
      {
        "label": "O2",
        "smiles": "[O][O]",
        "mole_fraction": 0.2,
        "reactive": true
      },
      {
        "label": "N2",
        "smiles": "N#N",
        "mole_fraction": 0.7,
        "reactive": false
      }
    ],
    "temperature_k": 1350,
    "pressure_pa": 101325,
    "termination": {
      "time_s": 1,
      "conversion": {
        "species": "CH4",
        "fraction": 0.9
      },
      "max_num_species": 50
    }
  },
  "resource": "cpu"
}'

{
  "species": [
    {
      "label": "CH4",
      "smiles": "C",
      "mole_fraction": 0.1,
      "reactive": true
    },
    {
      "label": "O2",
      "smiles": "[O][O]",
      "mole_fraction": 0.2,
      "reactive": true
    },
    {
      "label": "N2",
      "smiles": "N#N",
      "mole_fraction": 0.7,
      "reactive": false
    }
  ],
  "temperature_k": 1350,
  "pressure_pa": 101325,
  "termination": {
    "time_s": 1,
    "conversion": {
      "species": "CH4",
      "fraction": 0.9
    },
    "max_num_species": 50
  }
}

Sample data from the job catalog; long values are shortened here. Each job_name must be unique among your jobs.

Workflow inputs

Molecules (list)SMILES

Workflow outputs

ArchiveZIP
Kinetic mechanismYAML