For steric interactions, RMG previously included a limited set of gauche (i.e. 1,4) and 1,5-interactions. In the current version, these corrections have been re-organized into cyclic and non-cyclic non-nearest-neighbor interactions, following the addition of a new set of group additivity values for ring substituents by Ince et al. Ring strain can substantially affect the thermochemistry of many cyclic and polycyclic species. A previous limitation of the group additivity algorithm was that ring strain corrections would only be applied if there was an exact match to the molecule. To address this, a new estimation algorithm was developed to provide an estimate for the ring strain of any molecule based on a heuristic algorithm which decomposes the molecule into mono-and bicyclic substructures. Furthermore, the group additivity estimator in RMG has been significantly expanded for sulfur compounds, with the addition of 200 new group values for various C/H/O/S groups. These values were fitted from a collection of thermochemical data derived from quantum chemistry calculations.