CO adsorption on metal surfaces: A hybrid functional study with plane-wave basis set

We present a detailed study of the adsorption of CO on Cu, Rh, and Pt (111) surfaces in top and hollow sites. The study has been performed using the local density approximation, the gradient corrected functional PBE, and the hybrid Hartree-Fock density functionals PBE0 and HSE03 within the framework of generalized Kohn-Sham density functional theory using a plane-wave basis set. As expected, the local density approximation and generalized gradient approximation functionals show a tendency to favor the hollow sites, at variance with experimental findings that give the top site as the most stable adsorption site. The PBE0 and HSE03 functionals reduce this tendency. In fact, they predict the correct adsorption site for Cu and Rh but fail for Pt. However, even in this case, the hybrid functional destabilizes the hollow site by $50\mathrm{meV}$ compared to the PBE functional. The results of the total energy calculations are presented along with an analysis of the projected density of states.

Figure 1

(Color online) Orbital resolved electronic DOSs for the topmost Cu layer of the bare surface [panels (a)-d and (a)-sp] and for CO adsorbed at the top [panels (b)-d, (b)-sp, and (b)-CO] and hcp hollow sites [panels (c)-d, (c)-sp, and (c)-CO]. The DOSs are projected onto the metal $d$ states [panels (a)-d, (b)-d, and (c)-d: continuous, dotted, and dashed thick lines correspond to $d_{z^2}$, $d_{yz}+d_{xz}$, and $d_{xy}+d_{x^2-y^2}$ DOS, respectively], onto metal $\mathit{sp}$ states [panels (a)-sp, (b)-sp, and (c)-sp: continuous and dashed thin lines correspond to $s+p_z$ and $p_x+p_y$ DOS, respectively], and onto molecular orbitals [panels (b)-CO and (c)-CO: continuous, dotted, and dashed thick red lines correspond to $4\sigma +5\sigma$, $1\pi$, and $2{\pi }^{*}$ DOS, respectively]. The Fermi level is located at $0\mathrm{eV}$. In panel (a)-d, we show the one-electron energies of the $4\sigma$, $1\pi$, and $5\sigma$ molecular levels aligned with the Fermi level using bold tick marks.

Figure 2

(Color online) Orbital resolved electronic DOS (a) for the topmost Rh layer of the bare surface and for CO adsorbed at the (b) top and hcp (c) hollow site. See caption of Fig. 1 for details.

Figure 3

(Color online) Orbital resolved electronic DOS (a) for the topmost Pt layer of the bare surface and for CO adsorbed at the (b) top and hcp (c) hollow site. See caption of Fig. 1 for details.