Structural, Ordering, and Magnetic Properties of PtNi Nanoalloys Explored by Density Functional Theory and Stability Descriptors

Monometallic platinum and nickel nanoparticles and platinum-nickel nanoalloys are examined in the range 13-976 atoms from density functional theory calculations. A large set of competitive symmetries and morphologies are considered including the usual Mackay icosahedral, Marks decahedral, and truncated octahedral forms. A comparative analysis of relative stability order is addressed on the basis of four stability descriptors all predicted at the ab initio level from spin-polarized calculations including van der Waals interactions. For platinum nanoparticles, they unanimously conclude on the preference of truncated octahedral morphology in the range of 147-201 atoms. For nickel and platinum-nickel nanoclusters, three descriptors (cohesion energy, nanoparticle surface energy, and vibrational band center) also support such octahedral symmetry (with a skin-heart chemical ordering for nanoalloys), whereas the excess energy rather favors the icosahedral morphology (with multishell and core-shell arrangement). Such discrepancies feed the debate related to the impact of normalization on the predictive power of these descriptors and recall the high importance of validating theoretical models from a quantitative standpoint. This work invites the experimentalists to synthesize, characterize, and measure surface energetics of PtNi nanolloys in highly controlled operating conditions.