Journal of Computer Chemistry, Japan
Online ISSN : 1347-3824
Print ISSN : 1347-1767
ISSN-L : 1347-1767

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Electronic Structure and Stability of Binary Metal Cluster with Core-Shell Structure: Theoretical Approach
Nozomi TAKAGIRyoichi FUKUDAMasahiro EHARAShigeyoshi SAKAKI
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JOURNAL FREE ACCESS FULL-TEXT HTML Advance online publication

Article ID: 2018-0043

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Abstract

複数の金属元素からなる複合金属クラスターや微粒子は,貴金属減量触媒や卑金属触媒の候補として興味がもたれ,自動車排気ガス浄化触媒,燃料電池電極触媒などの実験分野で活発に研究がおこなわれている.新規な触媒の効率的な設計のためには,電子状態理論計算による複合金属クラスターの電子状態と安定構造, 分子吸着特性, 反応性の相関に対する知見が不可欠である.最近,銅とVIII族からXI族までの金属の複合クラスター(Cu32M6; M = Ru, Rh, Pd, Ag, Os, Ir, Pt, Au) ,および白金とVIII,IX族金属との複合クラスター(Pt42M13; M = Ru, Rh, Os, Ir)に関して統一的な電子状態理論研究がおこなわれ,シェルからコアへの電荷移動がコアシェル型構造の安定性を決める一つの重要な因子であることが報告された.本総説では,それらのコアシェル型構造の安定性と電子状態,安定性を支配する因子に関する議論をまとめて紹介する.

Figures
Scheme 1.

Schematic representation of (a) Cu37M isomers, (b) investigated isomers of Cu32M6, and (c) atomic labels of Pt42M13 clusters.

Adapted with permission from J. Phys. Chem. C, 121, 10514 (2017) and J. Phys. Chem. C, 121, 10514 (2017). Copyright (2018) American Chemical Society.

Figure 1.

 Segregation energy (Eseg) as a function of the difference in d orbital population of M between Cu37M (core) and the atomic ground state.

Reprinted with permission from J. Phys. Chem. C, 121, 10514 (2017). Copyright (2018) American Chemical Society.

Scheme 2.

Schematic representation of the most stable structure of Cu32M6 clusters.

Adapted with permission from J. Phys. Chem. C, 121, 10514 (2017). Copyright (2018) American Chemical Society.

Figure 2.

 (a) Relationship of interaction energy (Eint) between Pt42 shell and M13 core with the reverse of HOMO−LUMO energy gap (ΔεLU‐HO−1) and (b) relationship between Eseg and ΔεLU‐HO−1(Note: ΔεLU‐HO is the energy difference between the LUMO of M13 core and HOMO of Pt42 shell).

Reprinted with permission from J. Phys. Chem. C, 122, 9081 (2018). Copyright (2018) American Chemical Society.

Figure 3.

 HOMO (B3LYP-calculated orbital energy (in eV unit)) and DOSs (these DOSs were calculated by PBE-D2/plane wave basis sets using VASP program) of icosahedral Pt42M13 (M = Ru and Rh) and Pt55 clusters. The Fermi level is shown in the dashed line.

Adapted with permission from J. Phys. Chem. C, 122, 9081 (2018). Copyright (2018) American Chemical Society.

Tables
Table 1.  Relative energy (Erel in kcal/mol), NBO charge of M (q in e), and d orbital population (qd) and difference in d orbital population (Δqd) of M in Cu37M (M = Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au).
core-shell structure most stable non-core-shell structure
Cu37Ru
Erel 0.0 Cu37Ru (face) +13.6
q[Ru] -2.13
qdqd) 8.55 (+1.55)
Cu37Rh
Erel 0.0 Cu37Rh (face) +4.1
q[Rh] -1.79
qdqd) 9.22 (+1.22)
Cu37Pd
Erel 0.0 Cu37Pd (face) -6.2
q[Pd] -1.28
qdqd) 9.65 (+0.65)
Cu37Ag
Erel 0.0 Cu37Pd (corner) -20.5
q[Ag] -0.74
qdqd) 9.89 (−1.11)
Cu37Os
Erel 0.0 Cu37Os (face) +18.7
q[Os] -2.15
qdqd) 8.34 (+1.34)
Cu37Ir
Erel 0.0 Cu37Ir (face) +9.5
q[Ir] -1.99
qdqd) 9.04 (+1.04)
Cu37Pt
Erel 0.0 Cu37Pt (face) -1.0
q[Pt] -1.71
qdqd) 9.63 (+0.63)
Cu37Au
Erel 0.0 Cu37Au (corner) -15.3
q[Au] -1.14
qdqd) 9.87 (−0.13)
Cu38
Erel 0.0 - -
q[Cu] -0.60
qdqd) 9.86 (−0.14)
Table 2.  Relative energies (in kcal/mol) of isomers of Cu32M6.
a b c d e
core-shell fused-alloy phase-separated
Cu32Ru6a) 0.0 +16.4 +34.8 +80.0 +101.1
Cu32Rh6b) 0.0 +19.5 +18.3 +47.0 +104.3
Cu32Pd6b) 0.0 -6.1 -7.6 -33.4 +24.9
Cu32Ag6a) 0.0 -16.9 -19.0 -109.6 -108.1
Cu32Os6b) 0.0 +33.0 +76.5 +182.3 +128.9
Cu32Ir6a) 0.0 +29.4 +38.9 +93.6 +139.1
Cu32Pt6b) 0.0 -5.5 -12.4 -51.6 +35.3
Cu32Au6a) 0.0 -23.7 -26.9 -141.2 -97.6

a) Triplet state.

b) Singlet state

Table 3.  Relative energy (Erel in kcal/mol), NBO charge of M (q in e), and d orbital population (qd) and difference in d orbital population (Δqd) of M in Pt42M13 (M = Ru, Rh, Os, and Ir).
core-shell structure most stable non-core-shell structure
Pt42Ru13
Erel 0.0 Pt41Ruvertex(Ru12Pt)core +31.0
q[Rucore-1] -3.685
qdqd) 8.32 (+1.32)
q[Rucore-2] -1.433
qdqd) 8.03 (+1.03)
Pt42Rh13
Erel 0.0 Pt41Rhvertex(Rh12Pt)core +6.9
q[Rhcore-1] -3.220
qdqd) 9.13 (+1.13)
q[Rhcore-2] -1.774
qdqd) 9.26 (+1.26)
Pt42Os13
Erel 0.0 Pt41Osvertex(Os12Pt)core +61.2
q[Oscore-1] -2.274
qdqd) 8.45 (+2.45)
q[Oscore-2] -1.552
qdqd) 7.80 (+1.80)
Pt42Ir13
Erel 0.0 Pt41Iredge(Ir12Pt)core +41.5
q[Ircore-1] -1.425
qdqd) 8.23 (+1.23)
q[Ircore-2] -0.893
qdqd) 8.29 (+1.29)

Reprinted with permission from J. Phys. Chem. C, 122, 9081 (2018). Copyright (2018) American Chemical Society.

Table 4.  Averaged M-M distance (in angstrom) in the M6 core, averaged Cu-Cu distance in the C32 shell, and deformation energy (Edef in kcal/mol) of the Cu32 shell in Cu32M6(core).
M-M M-Cu Cu-Cu
core-core core-face core-corner face-corner corner-corner Edefa)
(i)b) (ii)c)
Cu38d) 2.572 2.629 2.540 2.550 2.556 2.541 -
Cu32Ru6d) 2.684 2.701 2.562 2.616 2.581 2.646 19.9
Cu32Rh6e) 2.772 2.663 2.528 2.618 2.591 2.644 23.9
Cu32Pd6e) 2.880 2.677 2.537 2.631 2.684 2.578 40.3
Cu32Ag6d) 2.837 2.808 2.590 2.640 2.740 2.526 46.8
Cu32Os6e) 2.657 2.694 2.577 2.624 2.566 2.677 22.9
Cu32Ir6d) 2.738 2.686 2.543 2.617 2.592 2.639 22.3
Cu32Pt6e) 2.946 2.669 2.533 2.644 2.711 2.677 50.9
Cu32Au6d) 2.937 2.791 2.580 2.652 2.784 2.513 61.7

a) Edef = E(Cu32-shell of Cu32M6(core)) − E(Cu32-shell of Cu38)

b) The Cu-Cu distance between corner Cu atoms in the same Cu (100) surface.

c) The Cu-Cu distance between corner Cu atoms in the different Cu (100) surfaces.

d) Triplet state.

e) Singlet state.

Reprinted with permission from J. Phys. Chem. C,121, 10514 (2017). Copyright (2018) American Chemical Society.

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