engleski

Ab initio calculations of the adsorption of Xe on Cu(111) and Pt(111) surfaces

We assess the role of van der Waals interactions in adsorption of Xe on Cu(111) and Pt(111) surfaces by complementing the density functional approach with the recently developed scheme for treating the long-range correlation effects [1]. Both systems are known to form a commensurate hexagonal overlayer at 1/3 coverage, with Xe atoms on top of the substrate atoms [2, 3]. We have performed ab initio density functional calculations with the GGA PBE functional, and used the calculated density to construct the dynamical polarisability of the substrate and determine the ensuing van der Waals contribution to the adlayer-substrate interaction.We find that such generalized DFT calculations, in which the van der Waals interactions make up a significant contribution to the overall correlation energy, yield the structural and dynamical properties of Xe adlayers, specifically the adsorption geometry and energy and the adlayer vibrational properties, that are in good agreement with experiments. Our calculations retrieve that the total-interaction-driven adsorption into commensurate phase causes dilation of the adlayer and a strong reduction of the intralayer radial force constants. This provides a first principles explanation of the observed dynamical properties of Xe adlayers, and in particular of the much debated dispersion of in-plane polarized vibrations, i.e. the softening of longitudinal phonon frequencies observed in Xe/Cu(111) and negligible dispersion in Xe/Pt(111). The obtained results demonstrate the potentiality of the described theoretical approach for treating a wide class of weakly adsorbed systems. [1] E. Hult, P. Hyldgaard, J. Rossmeisl, and B.I. Lundqvist, Phys. Rev. B 64, 195414 (2001). [2] J. Braun, D. Fuhrmann, A. Siber, B. Gumhalter, and Ch. Woell, Phys. Rev. Lett. 80, 125 (1998). [3] L.W. Bruch, A.P. Graham, and J.P. Toennies, Mol. Phys. 95, 579 (1999).

van der Waals interactions; Xe adsorption; Cu surface; Pt surface

nije evidentirano