Structural and electronic properties of Pt/Fe nanoclusters from EHT calculations

Fortunelli, Alessandro; Velasco, A. M.

doi:10.1016/s0166-1280(98)00597-1

Cited by 49 publications

(47 citation statements)

References 23 publications

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“…We focus on 55-atom clusters because the GM structure of the pure alkali clusters is well known, namely a perfect Mackay icosahedron, and it is interesting to analyse the stability of structurally magic clusters upon alloying. 8 Finally, an added interest of this work comes from the observation that Li interalkalies exhibit only phaseseparation behavior in the bulk limit, while Na-K and Na-Cs mixtures form an ordered Laves phase (MgZn 2 type). Thus the formation energy of Li-alkali bulk mixtures is positive and rapidly increases with the size mismatch, from a value of 56 meV/atom for Li-Na to a value of 227 meV/atom for LiCs.…”

Section: Introductionmentioning

confidence: 99%

Identifying structural and energetic trends in isovalent core-shell nanoalloys as a function of composition and size mismatch

Aguado

López²

2011

The Journal of Chemical Physics

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We locate the putative global minimum structures of Na x Cs 55−x and Li x Cs 55−x nanoalloys through combined empirical potential and density functional theory calculations, and compare them to the structures of 55-atom Li-Na and Na-K nanoalloys obtained in a recent paper [A. Aguado and J. M. López, J. Chem. Phys. 133, 094302 (2010)]. Alkali nanoalloys are representative of isovalent metallic mixtures with a strong tendency towards core-shell segregation, and span a wide range of size mismatches. By comparing the four systems, we analyse how the size mismatch and composition affect the structures and relative stabilities of these mixtures, and identify useful generic trends. The Na-K system is found to possess a nearly optimal size mismatch for the formation of poly-icosahedral (pIh) structures with little strain. In systems with a larger size mismatch (Na-Cs and Li-Cs), frustration of the pIh packing induces for some compositions a reconstruction of the core, which adopts instead a decahedral packing. When the size mismatch is smaller than optimal (Li-Na), frustration leads to a partial amorphization of the structures. The excess energies are negative for all systems except for a few compositions, demonstrating that the four mixtures are reactive. Moreover, we find that Li-Cs and Li-Na mixtures are more reactive (i.e., they have more negative excess energies) than Na-K and Na-Cs mixtures, so the stability trends when comparing the different materials are exactly opposite to the trends observed in the bulk limit: the strongly non-reactive Li-alkali bulk mixtures become the most reactive ones at the nanoscale. For each material, we identify the magic composition x m which minimizes the excess energy. x m is found to increase with the size mismatch due to steric crowding effects, and for Li x Cs 55−x the most stable cluster has almost equiatomic composition. We advance a simple geometric packing rule that suffices to systematize all the observed trends in systems with large size mismatch (Na-K, Na-Cs, and Li-Cs). As the size mismatch is reduced, however, electron shell effects become more and more important and contribute significantly to the stability of the Li-Na system.

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Section: Introductionmentioning

confidence: 99%

Identifying structural and energetic trends in isovalent core-shell nanoalloys as a function of composition and size mismatch

Aguado

López²

2011

The Journal of Chemical Physics

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“…Positive excess magnetic moments indicate that the formation of the corresponding oxidized nanoalloy is magnetically favorable as compared to an ideal mixture, and often presents a magnetism even higher than that associated with the two pure systems. We note that similar magnitudes are often used in the analysis of energetic trends or the compactness of nanoalloys (excess energy [ 55 ] and excess radius [ 56 ], respectively), but to our knowledge, the excess magnetic moment was not defined. In the lower panels of Figure 12 , Figure 13 and Figure 14 , we plot the excess magnetic moment of the binary TM oxide nanoalloys, as a function of the oxygen concentration m .…”

Section: Resultsmentioning

confidence: 99%

Tuning the Magnetic Moment of Small Late 3d-Transition-Metal Oxide Clusters by Selectively Mixing the Transition-Metal Constituents

et al. 2020

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Transition-metal oxide nanoparticles are relevant for many applications in different areas where their superparamagnetic behavior and low blocking temperature are required. However, they have low magnetic moments, which does not favor their being turned into active actuators. Here, we report a systematical study, within the framework of the density functional theory, of the possibility of promoting a high-spin state in small late-transition-metal oxide nanoparticles through alloying. We investigated all possible nanoalloys An−xBxOm (A, B = Fe, Co, Ni; n = 2, 3, 4; 0≤x≤n) with different oxidation rates, m, up to saturation. We found that the higher the concentration of Fe, the higher the absolute stability of the oxidized nanoalloy, while the higher the Ni content, the less prone to oxidation. We demonstrate that combining the stronger tendency of Co and Ni toward parallel couplings with the larger spin polarization of Fe is particularly beneficial for certain nanoalloys in order to achieve a high total magnetic moment, and its robustness against oxidation. In particular, at high oxidation rates we found that certain FeCo oxidized nanoalloys outperform both their pure counterparts, and that alloying even promotes the reentrance of magnetism in certain cases at a critical oxygen rate, close to saturation, at which the pure oxidized counterparts exhibit quenched magnetic moments.

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“…One effective tool in this respect is to exploit or enforce group symmetry, either point group symmetry or translational symmetry, as originally proposed in [50] and discussed in some detail in [16]. Given the exponential increase in the structural freedom of the system as a function of the size of the system, enforcing group symmetry entails a reduction in the system size by the order of the symmetry group, i.e., typically 10-20 in practically useful cases.…”

Section: Structure Prediction Methodsmentioning

confidence: 99%

“…To this purpose, the concept of mixing energy has been introduced in the nanoalloy field and has turned out to be very useful, see [13,45,50,70] Note that it is assumed that E alloy , E A , E B are global minimum energies, i.e., the lowest energies among all possible isomers. The mixing energy Δ[N A , N B ] can be easily generalized to ternary oxide nanoparticles thus providing also in this context a measure of how thermodynamically favorable is alloying at the given size and composition.…”

Section: The Promising Field Of Multi-component Oxidesmentioning

confidence: 99%

Atomistic and Electronic Structure Methods for Nanostructured Oxide Interfaces

Barcaro

Sementa

Negreiros

et al. 2016

Oxide Materials at the Two-Dimensional Limit

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An overview is given of methods for the computational prediction of the atomistic and electronic structures of nanoscale oxide interfaces. Global optimization approaches for structure prediction, together with total energy and electronic structure methods are reviewed and discussed. Our aim is to furnish conceptual instruments to select the optimal (i.e., the most accurate and least costly) method for treating a given system, and to understand the potentialities and limi-

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Structural and electronic properties of Pt/Fe nanoclusters from EHT calculations

Cited by 49 publications

References 23 publications

Identifying structural and energetic trends in isovalent core-shell nanoalloys as a function of composition and size mismatch

Identifying structural and energetic trends in isovalent core-shell nanoalloys as a function of composition and size mismatch

Tuning the Magnetic Moment of Small Late 3d-Transition-Metal Oxide Clusters by Selectively Mixing the Transition-Metal Constituents

Atomistic and Electronic Structure Methods for Nanostructured Oxide Interfaces

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