The distribution of d CC in Figure shows an elongation of these bonds, relative to the reference distance in pristine graphene (1.42 Å), as a result of the presence of the functional groups. Obviously, for the given degree of functionalization the d CC distribution depends on the spatial arrangement of the functional groups. The pronounced peak in the OGO models around the reference value corresponds to the graphene-like domain that is completely distinct from the oxidized region (small shoulder around 1.5 Å). The situation is reversed in the RGO models. Here, the main peak is located around 1.5 Å which approximately corresponds to the distance between sp 3 C atoms. A recent study has reported that, in contrast to our findings here, the distribution of d CC in random GO models is more diffuse. This discrepancy arises from the difference between the random GO configurations. Particularly, in the present random model we avoided adding functional groups to the edges of the periodic box, while the model in Ref. 25 did not have such a limitation. As a consequence our random models have relatively large graphene-like areas of sp 2 C atoms (cf. Figure ).