The structure of domains and domain walls in the low-temperature solid phase of stage-2 alkali-metal graphite intercalation compounds is studied using molecular-dynamics (MD) simulation and a model potential obtained from fitting to the liquid structure data. For RbC24, we find small domains of (s 7 × s 7) structure containing mostly seven Rb atoms and with domain walls consisting of (2×2) and (2×3) elemental plaquettes. These nanostructures provide a clear picture of the discommensurations and a consistent understanding of the x-ray-diffraction measurements. Based on the simulation results, we propose a periodic domain-wall model that explains very well the dominant features of the x-ray structure factor for both RbC24 and CsC24 when we allow for small changes in the planar density. © 1992 The American Physical Society.