Magic Polyicosahedral Core-Shell Clusters

Abstract

A new family of magic cluster structures is found by genetic global optimization, whose results are confirmed by density functional calculations. These clusters are Ag-Ni and Ag-Cu nanoparticles with an inner Ni or Cu core and an Ag external shell, as experimentally observed for Ag-Ni, and present a polyicosahedral character. The interplay of the core-shell chemical ordering with the polyicosahedral structural arrangement gives high-symmetry clusters of remarkable structural, thermodynamic, and electronic stability, which can have high melting points (they melt higher than pure clusters of the same size), large energy gaps, and (in the case of Ag-Ni) nonzero magnetic moments.

Quantum Monte Carlo studies of covalent and metallic clusters: Accuracy of density functional approximations

“…Clusters have naturally been the subject of numerous experimental and theoretical studies in recent years. [2][3][4][5][6][7][8] There are many potential technological applications of nanoclusters. Several metallic clusters have been shown to be very active catalysts 9,10 due to their high surface-area-to-volume ratios and unusual surface structures.…”

First principles study of bimetallic Ni13−nAgn nano-clusters (n = 0–13): Structural, mixing, electronic, and magnetic properties

“…Note that using empirical potential based DFT calculations, Ferrando et al first predicted a five-fold pancake geometry for the global total-energy minima of the 34-atoms NiAg alloy clusters. [49]It is also interesting to note from the Fig. 2 that the Ni-atoms at the core part are not symmetrically positioned around the center of the binary nano-clusters.…”

“…It is clearly seen that the coordination number for the Ni atoms is always higher than that of the Ag-atoms, which again support towards formation of core-shell structure with Ni atoms at the core and Ag atoms at the outer shell position, as reported earlier for the bigger sized Ni-Ag alloy clusters. [48,49,70] …”

“…We have also analyzed excess energy for the MESs of the NiAg alloyed clusters. The excess energy [49] for a binary Ni m Ag n cluster with respect to N = m + n bulk atoms has been defined as…”

“…[43][44][45][46][47]For example, global optimization of the NiAg nano clusters using some semi-empirical potentials with the tight-binding second moment approximation indicated poly-icosahedral structure of core-shell type for cluster sizes of 34 and 38 atoms. [48,49] On the other hand, the appearance of solid solution structured Ni-Ag nanoparticles, has also been discussed recently. [50] In the present work, we aim on shedding light to this confusing situation through DFT based electronic structure calculations.…”