Thermochemistry estimation has been expanded to estimate parameters for surface species by applying adsorption corrections. For a given surface species, the metal is first removed to obtain an estimate for the gas-phase species using existing methods (e.g., group additivity or libraries), then an adsorption correction is determined from a group additivity tree and added to the gas-phase value. Thermochemistry libraries are also supported for surface species. The RMG database currently contains a thermochemistry library with 21 adsorbates on nickel and a more recent library that has 69 H/C/O/N-containing adsorbates on platinum. By default, RMG uses binding energies for Pt(111), but energies for an arbitrary catalyst can be specified in the input file (Figure ). Adsorption corrections are then scaled appropriately based on the specified binding energies. Surface simulations require use of the new SurfaceReactor class. This module performs the reactor simulations necessary for the flux-based algorithm for model growth. It is modeled as a zero-dimensional, isothermal, isochoric batch reactor which tracks surface coverage in addition to gas-phase mole fractions. User specification of surface area to volume ratio and surface site density are required. For surface mechanism generation jobs, RMG will output separate gas-and surface-phase Chemkin mechanism files along with a single Cantera mechanism file.