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VULCAN

Photochemical & thermochemical kinetics for (exo)planetary atmospheres

VULCAN is an open-source 1D chemical kinetics code for planetary and exoplanetary atmospheres. It solves the coupled vertical continuity equations for every species, combining thermochemistry, photochemistry, and vertical transport to predict atmospheric composition far from chemical equilibrium. VULCAN can be used on its own, and is also integrated into the PROTEUS framework, a coupled simulation tool for the long-term evolution of rocky-planet atmospheres and interiors.

VULCAN running with real-time plotting

A VULCAN run converging to steady state.

Key features

  • Editable networks: chemistry is read from plain-text reaction files (hierarchical C–H–O, C–H–N–O, C–H–N–O–S); VULCAN auto-generates the source term and analytic Jacobian from the network at runtime.
  • Thermochemistry and photochemistry: forward reactions are reversed from NASA-9 thermodynamic data to recover equilibrium, while a two-stream radiative-transfer scheme drives photodissociation with temperature-dependent UV cross sections.
  • Full vertical transport: advection, eddy diffusion, and molecular plus thermal diffusion, with flexible boundary conditions.
  • Condensation and settling: saturation-based condensation/evaporation with gravitational particle settling for species such as H\(_2\)O, NH\(_3\), and sulfur.
  • Equilibrium initialization: compositions are initialized at chemical equilibrium with the embedded FastChem code.
  • Validated across regimes: benchmarked against hot Jupiters, Jupiter, and modern Earth, from reducing to oxidizing atmospheres.
  • Optional self-consistent climate: couples to the radiative–convective model AGNI to update the temperature structure during a run

Get started

  • Install VULCAN

    Set up VULCAN and compile FastChem, with optional Julia/AGNI for climate coupling.

    Installation guide

  • Run your first model

    Run the default model, edit the configuration, and plot the resulting profiles.

    First run

Citation and license

If you use VULCAN through PROTEUS, please cite the VULCAN theory papers listed in the publications and state the code version used. Citation metadata is provided in CITATION.cff.

VULCAN is released under the GPL-3.0 license.

FastChem

VULCAN embeds FastChem (Daniel Kitzmann & Joachim Stock) for equilibrium-chemistry initialisation of mixing ratios. FastChem carries its own license and should be cited independently. The relevant papers are listed in the publications. Please see the separate FastChem page for more information.

Licenses across the PROTEUS framework

Different components within the PROTEUS framework carry different licenses. Please find information about the use of licenses within the PROTEUS framework on the PROTEUS licence page.