AbstractWe derive exact properties of the inhomogeneous electron gas in the asymptotic classically forbidden region at a metal–vacuum interface within the framework of local effective potential energy theory. We derive a new expression for the asymptotic structure of the Kohn–Sham density functional theory (KS‐DFT) exchange‐correlation potential energyvxc(r) in terms of the irreducible electron self‐energy. We also derive the exact asymptotic structure of the orbitals, density, the Dirac density matrix, the kinetic energy density, and KS exchange energy density. We further obtain the exact expression for the Fermi hole and demonstrate its structure in this asymptotic limit. The exchange‐correlation potential energy is derived to bevxc(z→ ∞) = −αKS,xc/z, and its exchange and correlation components to bevx(z→ ∞) = −αKS,x/zandvc(z→ ∞) = −αKS,c/z, respectively. The analytical expressions for the coefficients αKS,xcand αKS,xshow them to be dependent on the bulk‐metal Wigner–Seitz radius and the barrier height at the surface. The coefficient αKS,c= 1/4 is determined in the plasmon‐pole approximation and is independent of these metal parameters. Thus, the asymptotic structure ofvxc(z) in the vacuum region is image‐potential‐like but not the commonly accepted one of −1/4z. Furthermore, this structure depends on the properties of the metal. Additionally, an analysis of these results via quantal density functional theory (Q‐DFT) shows that both the PauliWx(z→ ∞) and lowest‐order correlation‐kineticW(z→ ∞) components of the exchange potential energyvx(z→ ∞), and the CoulombWc(z→ ∞) and higher‐order correlation‐kinetic components of the correlation potential energyvc(z→ ∞), all contribute terms ofO(1/z) to the structure. Hence correlations attributable to the Pauli exclusion principle, Coulomb repulsion, and correlation‐kinetic effects all contribute to the asymptotic structure of the effective potential energy at a metal surface. The relevance of the results derived to the theory of image states and to KS‐DFT is also discussed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005