The electronic structure of a model bimetallic catalyst: symmetry-resolved density of states at \ ̄gG for Cu Ru(111)

The ruthenium hcp(0001) surface covered by a copper monolayer has become an important model system for investigating central questions regarding the catalytic behavior of bimetallic materials. We argue that the dominant modifications of the clean Ru surface electronic structure are relatively insensitive to the stacking of the layers near the surface, and we therefore carry out surface Green's function TB-LMTO computations to determine the symmetry- and layer-resolved density of states at k_{{norm of matrix}} = 0 ( \ ̄gG) for fcc Cu Ru(111), fcc Cu(111) and fcc Ru(111). At \ ̄gG there are two irreducible representations, a non-degenerate one, \ ̄gG₁, to which the s, p_z, and d_3z²-r² states belong and a doubly degenerate one, \ ̄gG₂, to which the p_x, p_y; d_xy, d_x²²t-y²; and d_xz, d_yz states belong. While we obtain various new surface resonances and bound states, our principal finding is that the Cu overlayer suppresses the upper \ ̄gG₂ subband of Ru at the surface. This finding suggests a simple theoretical interpretation of the X-ray spectroscopic observations and a possible basis for understanding the chemical behavior of this material.