A comprehensive simulation of the carbon structures and surface properties during bromination was performed, taking into account potential carbon edge-related pathways. This objective was achieved through the implementation of quantum chemical DFT and ab initio methods. By integrating the data obtained from quantum chemical modeling with empirical data from gas-phase halogenation of activated carbons, the size of carbon clusters, which serve as the structural units of carbon materials, were estimated in the context of thermodynamic Gibbs free energy considerations. The estimated concentration of double C=C bonds involved in electrophilic addition reactions is 1.0 to 1.5 mmol/g, which corresponds to 0.2 to 0.3 mmol/g of carbon clusters, representing five of the six peripheral C=C bonds of the reacting carbon cluster. Assuming that half of the carbon atoms in carbon solids are surface carbon and that carbon solids should consist only of carbon clusters with no functional groups, the average carbon cluster size is estimated to be between 140 and 210 atoms. Considering the heterogeneity of the carbon matrix and the possible presence of up to 1 mmol/g of oxygen-containing surface groups, it is reasonable to assume that the average carbon cluster size is likely to be considerably smaller. These estimates confirm the suitability of the proposed quantum chemical approaches for analyzing the reactivity of the carbon surface in activated carbon solids during bromination.