Modeling effects of subsurface tension on segregation:<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mi mathvariant="normal">Pt</mml:mi><mml:mn>25</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">Rh</mml:mi><mml:mn>75</mml:mn></mml:msub><mml:mrow><mml:mo>(</mml:mo><mml:mn>111</mml:mn><mml:mo>)</mml:mo></mml:mrow></mml:mrow></mml:math>oscillatory profile used as a test case

Polak, M.; Rubinovich, Leonid

doi:10.1103/physrevb.75.045415

Cited by 9 publications

(10 citation statements)

References 44 publications

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“…Consequently, Rh segregates to the subsurface, while Pt, due to its lower bulk bond energy ͑and preferential strengthening of its intrasurface bonds͒ segregates to the surface layer, resulting in a strongly oscillatory profile. Similar arguments have been introduced in our previous work based on the NRL-TB/FCEM approach 5 emphasizing that in alloys with a weak mixing tendency, such as Pt-Rh, it cannot be the origin of high-temperature oscillations. Hence, it arises from the opposite signs of the segregation driving forces ⌬ Pt-Rh ͑␥ m ͒ for the surface vs subsurface layers ͑Table II, bottom͒.…”

Section: B Role Of Surface-subsurface Bonding Variationssupporting

confidence: 74%

“…Our first attempts to go beyond simple empirical energetics as input in the FCEM for the study of alloy nanoclusters incorporated 4,5 elemental bond energies and their surfaceinduced variations as obtained by means of the Naval Research Laboratory-tight-binding method ͑NRL-TB͒. 6 However, it appears that quantitative evaluation of the role of elemental bond-energy variations in surface segregation in bulk alloys and alloy clusters necessitates more reliable energetics.…”

Section: Introductionmentioning

confidence: 99%

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Prediction of distinct surface segregation effects due to coordination-dependent bond-energy variations in alloy nanoclusters

Rubinovich

Polak

2009

Phys. Rev. B

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The first implementation of a recently introduced method based on the extraction of the coordination dependence of surface bond-energy variations ͑CBEV͒ from density-functional theory ͑DFT͒ computed puremetal surface-energy anisotropy is reported. In particular, polynomial functions fitted to DFT data computed previously for Pt, Pd, and Rh are used as input energetics for statistical-mechanical computations of Pt-Pd 923-atom cuboctahedron-cluster compositional structures ͑and Pt-Rh͑111͒ as a test case͒ using the free-energy concentration expansion method ͑FCEM͒. The major findings concern the roles of preferential strengthening of intrasurface and surface-subsurface interlayer bonds leading to quite unique segregation characteristics: ͑i͒ strong Pt segregation at certain ͑111͒ surface sites of the Pt-Pd clusters, accompanied, at relatively high overall Pt composition, by weaker Pt segregation forming Pt-Pd ordered ͑100͒ structure, whereas Pd segregates mainly at the edge and vertex sites; ͑ii͒ dominant Pd subsurface segregation. The high computation efficiency of the CBEV/FCEM approach allows the determination of the complete temperature dependence of atomic-exchange processes among surface sites, as well as between subsurface and deeper sites, reflected in the corresponding configurational heat-capacity curves. Compared to other approaches, the high transparency of this method helps to elucidate the origin of the distinct bond-energy-variation effects on site-specific segregation in alloy nanoclusters.

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Section: B Role Of Surface-subsurface Bonding Variationssupporting

confidence: 74%

Section: Introductionmentioning

confidence: 99%

Prediction of distinct surface segregation effects due to coordination-dependent bond-energy variations in alloy nanoclusters

Rubinovich

Polak

2009

Phys. Rev. B

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“…Alternatively, the clusters may show complete mixing. [9][10][11][12][13] In order to optimize the materials properties for a given application, it is of paramount importance to have an accurate understanding of the relation between cluster size on the one side and property on the other. Although experimental studies can provide much of this information, a full characterization of the experimentally studied systems is often lacking, suggesting that additional, theoretical studies can be helpful.…”

Section: Introductionmentioning

confidence: 99%

Structure and energetics of equiatomic K–Cs and Rb–Cs binary clusters

Hristova

Grigoryan

Springborg

2008

The Journal of Chemical Physics

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The basin-hopping algorithm combined with the Gupta many-body potential is used to study the structural and energetic properties of (KCs)(n) and (RbCs)(n) bimetallic clusters with N=2n up to 50 atoms. Each binary structure is compared to those of the pure clusters of the same size. For the cluster size N=28 and for the size range of N=34-50, the introduction of K and Rb atoms in the Cs alkali metal cluster results in new ground state structures different from those of the pure elements. In the size range N>/=38 the binary and pure clusters show not only structural differences, but they also display different magic numbers. Most of the magic Rb-Cs and K-Cs clusters possess highly symmetric structures. They belong to a family of pIh structures, where a fivefold pancake is a dominant structural motif. Such geometries have not been reported for alkali binary clusters so far, but have been found for series of binary transition metal clusters with large size mismatch. Moreover, tendency to phase separation (shell-like segregation) is predicted for both K-Cs and Rb-Cs clusters with up to 1000 atoms. Our finding of a surface segregation in Rb-Cs clusters is different from that of theoretical and experimental studies on bulk Rb-Cs alloys where phase separation does not occur.

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“…However, rather simplistic energetics were used in these FCEM computations involving elemental pair interactions estimated from the BOS model [4], with the assumption of equal distribution of the site energy among its nearest neighbour (NN) bonds [23][24][25][26]. More recently, we studied [27,28] alloy nanoclusters using the FCEM with improved energetics, which incorporates elemental bond energies and their surface-induced variations, obtained by means of the NRL Tight-Binding method [29]. Furthermore, as a test case we studied the role of such variations in the emergence of oscillatory segregation profiles in alloys with weak mixing or even demixing tendency [28].…”

mentioning

confidence: 99%

“…More recently, we studied [27,28] alloy nanoclusters using the FCEM with improved energetics, which incorporates elemental bond energies and their surface-induced variations, obtained by means of the NRL Tight-Binding method [29]. Furthermore, as a test case we studied the role of such variations in the emergence of oscillatory segregation profiles in alloys with weak mixing or even demixing tendency [28]. In particular, using FCEM with TB data, while neglecting alloying effects on elemental bond energies, a distinct two-layer oscillatory profile in Pt 25 Rh 75 (111) was obtained in reasonable agreement with previously reported experimental data [30].…”

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confidence: 99%

Coordination-dependent bond energies derived from DFT surface-energy data for use in computations of surface segregation phenomena in nanoclusters

Polak

Rubinovich

2011

IJNT

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Theoretical computations of alloy surface phenomena, such as elemental segregation, within atomic pair-interaction models, necessitate the use of reliable bond energies as input. This work introduces the idea to extract the coordination dependence of bond energies from density-functional theory (DFT) computed surface energy anisotropy. Polynomial functions are fitted to DFT data reported recently for surface energies of pure Pt, Rh and Pd. Compared to other approaches, the proposed method is highly transparent, and is expected to yield better insight into the origin of alloy segregation phenomena at surfaces of bulk and nanoclusters.

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Modeling effects of subsurface tension on segregation:Pt25Rh75(111)oscillatory profile used as a test case

Cited by 9 publications

References 44 publications

Prediction of distinct surface segregation effects due to coordination-dependent bond-energy variations in alloy nanoclusters

Prediction of distinct surface segregation effects due to coordination-dependent bond-energy variations in alloy nanoclusters

Structure and energetics of equiatomic K–Cs and Rb–Cs binary clusters

Coordination-dependent bond energies derived from DFT surface-energy data for use in computations of surface segregation phenomena in nanoclusters

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