Tailoring Electronic Structure Through Alloying: The Ag_nCu_34–n (n = 0–34) Nanoparticle Family

Abstract

Electronic structures of the free-standing coreÀshell (Cu@Ag) Ag n Cu 34Àn (n = 0À34) nanoalloy family are studied as a function of stoichiometry using ab initio total energy electronic structure calculations. Our calculations show that progressive alloying significantly alters the coordination distribution, bond lengths, formation energies, and the electronic densities of states. Changes in coordination and elemental environment are reflected in the electronic densities of states, which broaden or narrow as a result of hybridization between the Cu and the Ag atoms. The densities of states of Ag atoms in Ag-rich nanoparticles show large broadening when a single Cu atom is introduced, followed by substantial deviation of the position of the center of d states from that of the pristine (Ag 34 ) nanoparticle. Such deviation is found to persist for nonsymmetric nanoparticles. The calculated HOMOÀLUMO gaps vary between 0.2 and 0.9 eV within the family. The magnitude of the gaps is found to be strongly dependent on the geometric structure determined by the species ratio: the particles belonging to two ends of the NP family have relatively small gaps, and no overriding symmetry, whereas those toward the middle of the family exhibit high symmetry and larger gaps. The calculated ionization energies show no monotonic dependence on the Cu-to-Ag ratio and fluctuate within 500 meV as the stoichiometry changes.

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