Structural transformation in Pd nanoclusters induced by Cu doping: an ADFT study

Abstract

Context

Transition metal nanoparticles have gained great importance due to their promising applications in various fields such as energy, electronics, medicine, and agriculture. For these applications, materials with outstanding properties are currently required. Therefore, different strategies have been established to improve the properties of pure nanoparticles such as alloying, doping, and formation of composites. Among these strategies, doping is gaining great importance because it has been demonstrated that doped nanoparticles have better properties than pure nanoparticles. Therefore, it is essential to know the role of doping on the structures and properties of clusters with more than 16 atoms. Consequently, in this study, we propose a theoretical study of structures and properties focusing on pure Pd₁₉, Cu-doped Pd₁₈ (Pd₁₈Cu), and Cu₂-doped Pd₁₇ (Pd₁₇Cu₂) nanoclusters and thus elucidate the role of Cu atoms on the structures and properties of larger doped Pd nanoclusters than those already presented in the literature. We have selected a nanocluster with 19 atoms since the most stable structure of this system is characterized by defined shapes such as octahedron or double-icosahedron.

Methods

Ground state structures and properties of Pd₁₉, Pd₁₈Cu, and Pd₁₇Cu₂ nanoclusters were studied using the auxiliary density functional theory (ADFT), as implemented in the deMon2k code. For obtaining the ground state structures of Pd₁₉, Pd₁₈Cu, and Pd₁₇Cu₂ nanoclusters, several dozen initial structures were taken along Born–Oppenheimer molecular dynamics (BOMD) trajectories and subsequently optimized without symmetry restrictions. The optimizations were performed with the revised PBE functional in combination with TZVP-GGA for the Cu atoms and using an 18-electron QECP|SD basis set for the Pd atoms. Different energetic and electronic properties were calculated for the most stable structures of Pd₁₉, Pd₁₈Cu, and Pd₁₇Cu₂ nanoclusters. Interestingly, when the Pd nanocluster is doped with two Cu atoms (Pd₁₇Cu₂), there is a structural transition, because the most stable structures for Pd₁₉ and Pd₁₈Cu are icosahedral. While the Pd₁₇Cu nanocluster is characterized for a double-icosahedral-base structure. The binding energy per atom increases when the Cu concentration in the nanoclusters increases. According to the HOMO–LUMO gap, the chemical reactivity of the nanoclusters tends to increase as the Cu content in the nanoclusters increases.