Micha Polak

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Chemical ordering in face-centered-cubic-like PdPt nanoparticles consisting of 38-201 atoms is studied via density-functional calculations combined with a symmetry orbit approach. It is found that for larger particles in the Pd-rich regime, Pt atoms can segregate at the center of the nanoparticle (111) surface facets, in contrast with extended systems in(More)
Nanoconfinement entropic effects on chemical equilibrium involving a small number of molecules, which we term NCECE, are revealed by two widely diverse types of reactions. Employing statistical-mechanical principles, we show how the NCECE effect stabilizes nucleotide dimerization observed within self-assembled molecular cages. Furthermore, the effect(More)
Phase-separation second-order transitions in binary alloy particles consisting of ∼1000 up to ∼70 000 atoms (∼1-10 nm) are modeled focusing on the unexplored issue of finite-size scaling in such systems, particularly on evaluation of correlation-length critical exponents. Our statistical-thermodynamic approach is based on mean-field analytical expression(More)
A new coarse-grained layer model (CGLM) for efficient computation of axially symmetric elemental equilibrium configurations in alloy nanoparticles (NPs) is introduced and applied to chemical-order transitions in Pt-Ir truncated octahedra (TOs) comprising up to tens of thousands of atoms. The model is based on adaptation of the free energy concentration(More)
Recently we predicted that when a reaction involving a small number of molecules occurs in a nanometric-scale domain entirely segregated from the surrounding media, the nanoconfinement can shift the position of equilibrium toward products via reactant-product reduced mixing. In this Letter, we demonstrate how most-recently reported single-molecule(More)
With current developments in nanoscience and nanotechnology, experimental studies of reactions in confined nanospaces have been emerged. Thus, a variety of tailor-made “nanoreactors” have been fabricated: (i) molecular capsules, held together either by covalent bonding or by self-assembly via weaker interactions such as metal coordination and hydrogen(More)
Chemical order in platinum-iridium truncated-octahedron nanoparticles as a model system was studied using coordination-dependent bond-energy variations (CBEV) and the statistical-mechanical free-energy concentration expansion method (FCEM) adapted for handling axially symmetric structures. Pt-Ir side-separated ("Quasi-Janus", QJ) configurations are found to(More)
The equilibrium state of a reaction mixture comprised of a small number of molecules is modeled for three different nanoconfined systems. The issue is relevant to several advanced routes for the synthesis of encapsulated organic molecules, metallic or inorganic nanoclusters, and other nanoscale structures. Canonical-ensemble based formulations and(More)