Ab-initio study of the structure of Pd(110)-c(4 x 2)-benzene

From first principle calculations we have determined the structure of the P d(110)-c(4 x 2)-benzene system for three azimuthally different orientations of the benzene molecule (two with C-2v and one with C-2 symmetry). For all cases, in the relaxed structure the benzene molecule loses its planar geom etry since the C-H bonds appreciably bend upwards, the carbon hexagon loses planar geometry too and exhibits inequivalent C-C bond lengths, and the su bstrate is slightly buckled. We discuss the calculated geometries in terms of benzene-substrate interactions and predict a C-2 symmetry of the adsorbe d molecule.