Thermal Properties And Ground-State Structures Of Pure And Alloy Nanoclusters Via Molecular Dynamics Simulation
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Date
2018-03
Authors
Ong, Yee Pin
Journal Title
Journal ISSN
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Publisher
Universiti Sains Malaysia
Abstract
The study of thermal properties of nanoclusters via molecular dynamics simulation is a common research topic in computational physics. However, the methods of post-processing and determining the pre-melting and melting range of nanoclusters at specific composition differ in every research. In this thesis, the study of thermal properties was started by obtaining the ground-state structure of 38-atoms gold-platinum nanoclusters of various composition (where ) using Parallel Tempering Multicanonical Basin Hopping plus Genetic Algorithm (PTMBHGA). Bimetallic nanocluster with D6h symmetry has been selected for further investigation in the thermal properties, as it is the most stable bimetallic nanocluster studied in this thesis. To study the melting mechanism of the clusters, a molecular dynamics code known as Brownian type isothermal molecular dynamics (BTIMD) was used. Specific heat, and Lindemann index, , which are the common descriptors used to monitor the melting behaviour of clusters were calculated for . The curve revealed that the melting of this nanocluster commenced between 1000 K and 1050 K. Both and curves showed drastic increase at 700 K to 800 K, indicating the presence of pre-melting phase in nanoclusters. To scrutinize the pre-melting phenomena, ultrafast shape recognition (USR) code has been introduced. The data was plotted into atomic-distance plots and probability distribution function of shape similarity index. Both these two results independently proved that the pre-melting stage occurred between 760 K and 770 K. Various independent computational methods attempted in this thesis shown convergent results in the pre-melting and melting range of the studied nanoclusters. Amongst these methods, the USR approach provided the most detailed insight to the melting behaviour of the nanaoclusters. It has proven itself to be a more precise as indicator compared to specific heat, and Lindemann index, .
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Keywords
Thermal properties and ground-state structures , alloy nanoclusters via molecular dynamics simulation