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Noble metal nanoparticles with core-shell structure play important roles for nano-scale catalysts. Recently, the core-shell nanoparticles has been reported in the binary Au-Pd which have high catalytic activity for hydrogen or CO [1-3]. The Au-core and Pd-shell (Au@Pd) nanoparticles have interface structures of the epitaxial relationship between core and shell [4] and thin Pd overlayers on Au(100) [5] and (111) [6]. The first-principles study of slabs have been reported [7]. In this paper, we perform first-principles calculations of Pd/Au slab interfaces and Au@Pd core-shell nanoparticles using the projector augmented-wave (PAW) program code QMAS (Quantum MAterials Simulator). We clarify the atomic and electronic structures and discuss the effect of surface and interface structures for the reactivity of atomic hydrogen and CO. For the slab interfaces Pd on Au(100) and (111), the energy analysis of the lattice strain shows that the Pd overlayers has a pseudomorphic structure on Au with lateral expansion with respect to bulk Pd. The atomic structure near the interface is rather stable for the intermixing configurations of Au and Pd. The adsorption energies of hydrogen and CO tend to have a peak at two Pd overlayers system, which is in agreement with the previous study [7]. The atomic and electronic structures of Au@Pd (N=13, 55, 147) nanoparticles are interesting feature. The corner atoms of Pd-shell show large displacement and the charge density distribution near the corner atom of Pd-shell is relatively large change. The local reactivities of H and CO are large near the corner atoms. This work was partially supported by the Japan Society for the Promotion of Science (JSPS) Research (Grant-in-Aid for Scientific Research B, No.17360314). [1] Y. Mizukoshi et al., J. Phys. Chem. B, 104, 6028 (2000).[2] H. Takatani et al., Mater. Sci. Forum 445-6, 192 (2004).[3] D. I. Enache et al., Science 311, 362 (2006).[4] T. Akita et al., Catal. Today, submitted. [5] A. L. N. Pinheiro et al., Surf. Sci. 600, 641 (2006). [6] L. Piccolo et al., Surf. Sci. 600, 4211 (2006). [7] A. Roudgar and A. Gross, J. Electroanal. Chem. 548, 121 (2003).
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