Surface structure of K/Pd(100) and the effect of H coadsorption: Density functional theory calculations

Abstract

We have performed density-functional theory calculations to study the atomic structure of the K/Pd(100)-p(2 x 2) and -c(2 x 2) surfaces formed at 0.25 ML and 0.5 ML, respectively. We find that K atoms prefer the hollow site with the K adsorption height 2.44 angstrom for p(2 x 2) and 2.50 angstrom c(2 x 2). The first interlayer spacing (d(12)) of the Pd(100) substrate appears slightly contracted from the bulk value as Ad(12) = -0.8% and -0.3% for p(2 x 2) and c(2 x 2), respectively. The calculated contraction Delta d(12) = -0.3% for c(2 x 2) is not in accord with the expansion Ad(12) = +1.3% reported by a low-energy electron diffraction (LEED) study. As the origin of this difference, a possibility of hydrogen contamination of the surface sample used in the LEED study is suggested: Our calculations show that the d(12) of K/Pd(100)-c(2 x 2) increases linearly with the coverage of H coadsorption, which leads to an estimation for the H coverage of the surface sample as 0. 1-0.4 ML. (c) 2006 Elsevier B.V. All rights reserved.