Adsorption structures of tetracene on the Ru(1010) surface has been investigated by means of ab initio density functional theory (DFT) calculations. Several adsorption geometries of tetracene on Ru(1010) were examined in details. The optimized structures have an adsorption energy of 4.23 eV for tetracene adsorbed between the top and the second Ru atoms rows with its long molecular axis along the [1110] direction, and a slightly smaller adsorption energy of 4.19 eV for tetracene adsorbed with its long axis perpendicular to [1110], consisting well with the adsorption structures observed in the scanning tunneling microscopy (STM) measurements for tetracene overlayer on Ru(1010). By Comparing DOS before and after tetracene adsorption, we suggest that the coupling of the substrate d-band and the filled p-orbitals of tetracene determines tetracene adsorption on the Ru(1010) surface. (c) 2006 Elsevier B.V. All rights reserved.