CO adsorbed on Cu(001): A comparison between local density approximation and Perdew, Burke, and Ernezerhof generalized gradient approximation

Adsorption energetics, structural and vibrational properties of the Cu(001) -c(2 X 2)-CO system are studied with periodic slab calculations within dens ity functional theory in the local density (LDA) and generalized gradient ( GGA) approximations by using ultrasoft pseudopotentials. The recent express ion of Perdew, Burke, and Ernzerhof (PBE) has been used as the GGA function al [Phys. Rev; Lett. 77, 3865 (1996)]. The fully relaxed geometry of the sy stem is determined for different adsorption sites,of the CO molecule; unlik e LDA, PBE-GGA predicts correctly the on-top adsorption site of the molecul e. C-O and Cu-CO bond lengths, stretching frequencies, Cu-layer displacemen ts, chemisorption energies, and work functions are computed under both appr oximations and are compared to the experimental values. LDA. gives accurate ,values for the C-O equilibrium distance and the corresponding stretching f requency, while PBE-GGA better describes the adsorption bond and all the re maining properties. (C) 2001 American Institute of Physics.