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Standard enthalpies, entropies, and heat capacities are calculated for more than 14,000 halogenated species using a high-fidelity automated thermochemistry workflow. This workflow generates conformers at density functional tight binding (DFTB) level, optimizes geometries, calculates harmonic frequencies, and performs 1D hindered rotor scans at DFT level, and computes electronic energies at G4 level. The computed enthalpies of formation for 400 molecules show good agreement with literature references, but the majority of the calculated species have no reference in the literature. Thus, this work presents the most accurate thermochemistry for many halogenated hydrocarbons to date. This new dataset is used to train an extensive ensemble of group additivity values (GAV) and hydrogen bond increment groups (HBI) within the Reaction Mechanism Generator (RMG) framework. On average, the new group values estimate standard enthalpies for halogenated hydrocarbons within 3 kcal/mol of their G4 values. To demonstrate the significance of RMG’s improved halogen thermochemistry, a model for C3H2F3Br (2-BTP) is generated, and flame speeds are compared to a literature mechanism. A significant contribution towards the automation of detailed modeling of halogenated hydrocarbon combustion, this research provides thermochemical data for thousands of novel halogenated species and presents a comprehensive set of halogen group additivity values.