Formation of dust structures in a capacitively coupled RF discharge was studied with a self-consistent particle simulation. For this purpose 3D Particle-in-Cell code with Monte Carlo collisions (PIC MCC), resolving also the sheath in front of the wall including all relevant species (neutrals, ions, electrons) and their reactions was developed and applied.In the simulation dust particles trapped in the sheath over the lower electrode form vertical strings, in which negative particles are attracted due to polarization of the ion flow (wake-field effect). A quasi 2 dimensional (simple hexagonal) structure is formed by the dust in which flat layers with hexagonal symmetry are vertically aligned due to the unidirectional ion background flow towards the electrode in the sheath.Particle-Particle/Particle-Mesh (P3M) algorithm was introduced into the model in order to accurately resolve the close-range interaction between the dust grains and plasma particles. Charging of the dust grains due to absorption of plasma particles was studied self-consistently with this model.