Computational Studies of Transition Metal Nanoalloys (eBook)

Computational Studies of Transition Metal Nanoalloys 4
Supervisor’s Foreword 8
Acknowledgments 9
Contents 10
1 Introduction 14
1.1…Clusters: Overview and Applications 15
1.2…Nanoalloys 16
1.2.1 Homotops 17
1.2.2 Segregation in Nanoalloys 17
1.3…Experimental Background: From Synthesis to Cluster Characterisation 19
1.4…Second and Third Rows Transition Metal Nanoalloys 20
1.4.1 Pd--Pt Clusters 20
1.4.2 Pd--Au Clusters 21
1.4.3 Ag--Pt Clusters 21
1.4.4 Ag--Au Clusters 22
1.5…Chemisorption on Single Metal and Bimetallic Clusters 22
References 24
2 Theoretical Background and Methodology 27
2.1…Modelling Metal Clusters and Nanoalloys 27
2.1.1 Potential Energy Surfaces 28
2.2…Theoretical Methods 28
2.2.1 The Gupta Potential 28
2.2.2 Early Density Functional Theory: Thomas Fermi Model 29
2.2.3 Modern Density Functional Theory 31
2.2.4 Functionals and Basis Sets 34
2.3…Global Optimization Techniques 35
2.3.1 The Birmingham Cluster Genetic Algorithm 35
2.3.2 The Basin-Hopping Monte Carlo Algorithpotential energy surface (PES)m 38
2.3.3 Shell Optimization Routine 39
2.3.4 Combined EP-DFT Approach 39
2.4…Energetic Analysis 40
References 42
3 34-Atom Pd--Pt Clusters 44
3.1…Introduction 44
3.2…Computational Details 44
3.3…Results and Discussion 45
3.3.1 Gupta Potential Calculations on PdmPt34& !nbsp
3.4…DFT Calculations 48
3.4.1 Composition Pd24Pt10 49
3.4.2 Segregation Effects for Pd17Pt17 Clusters 51
3.4.3 Analysis of the Dh--cp(DT) Structure 52
3.4.4 Conclusions 54
References 55
4 98-Atom Pd--Pt Nanoalloys 56
4.1…Introduction 56
4.2…Computational Details 56
4.3…Results and Discussion 57
4.3.1 Comparison of Global Minimum Structures for 98-Atom Pd--Pt Nanoalloys 57
4.3.2 Analysis of the Leary Tetrahedron 61
4.3.3 Onion-Like Structures 62
4.3.4 Competition Between Different Structural Families 62
4.4…Conclusions 63
References 64
5 38-Atom Binary Clusters 65
5.1…Introduction 65
5.2…Computational Details 67
5.3…Results and Discussion 68
5.3.1 Structural Families 69
5.3.2 Composition Dependence of the Mixing Energy 72
5.3.3 Pd--Pt Clusters 72
5.3.4 Segregation Effects in Pd--Pt Clusters 74
5.3.5 Ag--Pt Clusters 75
5.3.6 Segregation Effects in Ag--Pt Clusters 75
5.3.7 Pd--Au Clusters at Compositions 14--24 and 6--32 76
5.3.8 Pd--Au Clusters at Compositions 24--14 and 32--6 78
5.3.9 Segregation Effects in Pd--Au Clusters 79
5.3.10 Ag--Au Clusters 79
5.3.11 Segregation Effects in Ag--Au Clusters 81
5.4…Conclusions 84
References 85
6 Chemical Ordering of 34-Atom Pd--Pt Nanoalloys 87
6.1…Introduction 87
6.2…Computational Details 90
6.2.1 Genetic Algorithm 90
6.3…Results and Discussion 92
6.3.1 DFT Study of (Pd--Pt)N/2 Clusters (N = 2--20) 92
6.3.2 Gupta Potential Study of (Pd--Pt)N/2 Clusters (N = 2--20) for Potentials Ia, Ib and Ic 95
6.3.3 Gupta Potential Study of 34-Atom Pd34Pt34minusm Clusters for Potentials Ia, Ib and Ic 95
6.3.4 Detailed Study of 34-Atom PdmPt34minusm Clusters for Variable Gupta Potential Weights 98
6.3.5 Structural Motifs 99
6.3.6 Segregation 104
6.3.7 Study of Interfacial Areas in Segregated Bimetallic Clusters 104
6.3.8 Derivation of the Interfacial Area Formulae 107
6.3.8.1 Core--Shell Segregation 107
6.3.8.2 Spherical Cap Segregation 108
6.3.8.3 Ratio of Interfacial Areas 109
6.4…Conclusions 109
References 111
7 Theoretical Study of Pd--Au Clusters 112
7.1…Introduction 112
7.2…Computational Details 113
7.2.1 Genetic Algorithm 113
7.2.2 Pd--Au Parameters 113
7.3…Results and Discussion 115
7.3.1 Gupta Potential Calculations on (Pd--Au)N/2 Clusters (N = 2--50) 115
7.3.2 DFT Calculations on (Pd--Au)N/2 Clusters (N = 2--25) 119
7.3.3 Structural Analysis 120
7.4…34-Atom Pd--Au Clusters 120
7.5…38-Atom Pd--Au Clusters 123
7.6…DFT Investigation of Segregation in 34- and 38-Atom Pd--Au Clusters 131
7.7…Large Pd--Au Nanoclusters, N = 98 Atoms 133
7.7.1 Global Optimizations of 98-Atom Pd--Au Clusters 133
7.7.2 Leary Tetrahedron Structure 135
7.8…Conclusions 136
References 141
8 Chemisorption on Metal Clusters and Nanoalloys 142
8.1…Introduction 142
8.1.1 Experimental and Theoretical Studies on Chemisorption 142
8.2…Chemisorption of CO and H on Pd, Pt and Au Nanoclusters 143
8.2.1 Energetic Analysis 144
8.2.2 Computational Details 146
8.3…Results 147
8.4…Chemisorption of CO and H on Bimetallic Clusters 153
8.5…Conclusions 154
References 155
9 Conclusions and Future Work 157
References 159
Index 160