Relative stability of icosahedral and cuboctahedral metallic nanoparticles
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Relative stability of icosahedral and cuboctahedral metallic nanoparticles A. V. Myshlyavtsev • P. V. Stishenko
Received: 13 November 2012 / Accepted: 15 February 2013 / Published online: 8 March 2013 Ó Springer Science+Business Media New York 2013
Abstract The size and form of metallic nanoparticles (NPs) significantly affects their adsorptive, chemical, and catalytic activity. One of the most interesting nanoscale size effects is the transition from icosahedral to octahedral forms with growth in the NP size. We compared the stability of icosahedral, decahedral and cuboctahedral NPs made from eight metals Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au using the local optimization of total energy, which was computed from the tight-binding second moment approximation and quantum Sutton–Chen potentials. The obtained results predicted that the icosahedral form would be most stable for Ni, and least stable for Au. For Rh, and especially for Ir, a strong dependency of the stability of the different forms on the NP size was revealed. Keywords Nanoparticles Icosahedral Cuboctahedral Energy minimization
1 Introduction Metallic nanoparticles (NPs) show numerous interesting chemical properties, including high catalytic activity (Cuenya 2010). From theoretical and experimental considerations, it is clear that one of the most important factors influencing the chemical activity is the adsorption of different molecules on the NP surfaces. Recent advances in computing technologies, ab initio models, and algorithms have resulted in a deeper understanding of the chemical A. V. Myshlyavtsev P. V. Stishenko (&) Omsk State Technical University, Omsk, Russia e-mail: [email protected] A. V. Myshlyavtsev e-mail: [email protected]
properties of NP faces. Much effort has been devoted to the investigation of different adsorption sites on different faces of metal crystals and NPs; for example, quantitative ab initio evaluations have been made of adsorption energies, site geometries and vibrational characteristics (Cuenya 2010; Martin et al. 1995; Han et al. 2008; Jiang et al. 2009; Myshlyavtsev and Stishenko 2010). The distribution of different active adsorption sites on the NP surface strongly depends on the NP size and shape, and differs significantly from the distribution on bulk surfaces. The size and shape of NPs therefore have significant effects on their adsorptive, chemical, and catalytic activity. 1.1 Five-fold symmetry quasicrystals and face-centered cubic crystals One of the most obvious manifestations of size effects in metals is the preference for fivefold symmetry (5fs) structures in small particles, instead of the face centered cubic (fcc) crystal structure observed in bulk metals. NPs with 5fs structure have icosahedral or decahedral shapes, or truncated modifications of these forms. The surface of ideal icosahedral or decahedral NPs consists only of (111) faces, which are close-packed, and are more energetically favorable than other faces. NPs with fcc crystal lattices have octahedral or truncated octahedral shapes. Ideal
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