Density functional theory calculations of tetracene on low index surfaces of copper crystal

This paper carries out the density functional theory calculations to study the adsorbate--substrate interaction between tetracene and Cu substrates (Cu (110) and Cu (100) surface). On each of the surfaces, two kinds of geometry are calculated, namely `flat-lying' mode and `upright standing' mode. For `flat-lying' geometry, the molecule is found to be aligned with its longer molecular axis along close-packed direction of the substrate surfaces. For `upright standing' geometry, the long axis of tetracene is found to be parallel to the surface normal of the substrate on Cu (110) surface. However, tetracene appears as `tilted' mode on Cu (100) surface. Structures with `flat-lying' mode have much larger adsorption energy and charge transfer upon adsorption than that with `upright standing' mode, indicating the preference of `flat-lying' geometry on both Cu (110) and Cu (100) surface.