We have studied the atomic geometries and electronic properties of the tris-(8-hydroxyquinoline) aluminum (Alq(3))/Al interface using density functional calculations. The calculated interface dipoles agree reasonably well with the experiments and the origin of the interface dipole formation mainly comes from the alignment of the permanent dipoles of Alq(3) molecules. The HOMO levels of the Alq(3) molecules significantly depend on the orientation of the Molecular permanent dipoles and the interfacial gap state observed by experiments is ascribed to the co-existence of the two orientations of the molecular dipoles. (c) 2006 Elsevier B.V. All rights reserved.