| Summary: | 碩士 === 國立中央大學 === 物理研究所 === 96 === The isothermal Brownian-type molecular dynamics simulation has been applied to study the melting behavior of bimetallic clusters. It was found that the specific heat and Lindermann-like parameter customarily used in bulk system to describe solid-liquid transition show incongruity in the prediction of melting temperature, T_{melt}. The underlying mechanisms that lead to the incompatibility of melting temperatures deduced from these two quantities were analyzed further. To gain insight into the melting behavior, we calculated in addition the velocity autocorrelation function and its Fourier transform, the power spectrum, to extract separately the melting temperature. It appears that the melting temperature inferred from the latter quantities is closer to that deduced from the principal peak position of specific heat. Two bimetallic clusters, Ag₁Cu₁₃ and Au₁Cu₁₃, were selected for thorough investigation. For the cluster morphology, we carried out a quantitative comparison of Ag₁Cu₁₃, Au₁Cu₁₃ and Cu₁₄ to locate the atomic distribution and contrasted between a bimetallic cluster and a pure cluster to learn the thermal reaction of atoms, in particular the impurity atom in the bimetallic cluster. On analyzing the dynamical data, we observed at a lower temperature (T≪T_{melt}) migrational relocation of atoms whose dynamics was superimposed by permutations between atoms at an intermediate temperature (T<T_{melt}), and at a higher temperature (T≈T_{melt}), the atoms behave liquid- or even gas-like.
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