The structural and electronic properties of Cu segregation in aluminum are studied in the framework of the density functional theory, within the projector augmented plane-wave method and both its local density approximation (LDA) and generalized gradient approximation (GGA). We first studied Al-Cu interactions in bulk phase at low copper concentration (<=�3.12%: at). We conclude to a tendency to the formation of a solid solution at T�=�0�K. We moreover investigated surface alloy properties for varying compositions of a Cu doped Al layer in the (111) Al surface then buried in an (111) Al slab. Calculated segregation energies show unstable systems when Cu atoms are in the surface position (position 1). In the absence of ordering effects for Cu atoms in a layer (xCu�=�1/9 and xCu�=�1/3), the system is more stable when the doped layer is buried one layer under the surface (position 2), whereas for xCu�=�1/2 to xCu�=�1 (full monolayer), the doped layer is more accommodated when buried in the sub-sub-surface (position 3). First stage formation of GP1- and GP2-zones was finally modeled by doping (100) Al layers with Cu clusters in a (111) Al slab, in the surface then buried one and two layers under the surface. These multilayer clusters are more stable when buried one layer beneath the surface. Systems modeling GP1-zones are more stable than systems modeling GP2-zones. However the segregation of a full copper (100) monolayer in an (100) Al matrix shows a copper segregation deep in the bulk with a segregation barrier. Our results fit clearly into a picture of energetics and geometrical properties dominated by preferential tendency to Cu clustering close to the (111) Al surface.