合金金屬叢集的溫度效應; The thermal properties of bimetallic clusters

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题名:	合金金屬叢集的溫度效應;The thermal properties of bimetallic clusters
作者:	顏聰文;Chung-Wen Yen
贡献者:	物理研究所
关键词:	有限大系統;分子動力學;合金金屬叢集;metallic cluster;finite system;ensemble difference
日期:	2005-11-26
上传时间:	2009-09-22 10:56:31 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	我們使用了brownian-type分子動力學來分析研究合金金屬叢集的的溫度效應這篇文章主要探討兩個議題: 其一不同系綜在有限大系統下是否等價? 我們計算並比較Cv(比熱)和 δ(lindemann index)這兩個物理量分別在正則(本篇)和微正則(文獻)系綜的數值結果 ,發現不同系綜存在著一些普適性的差異其二這兩個物理量再同一系綜預測溶化溫度上也出現不一致,我們試著用能量分布圖和rij來解釋背後機制,獲得非常令人滿意的結果 The brownian-type molecular dynamics has been applied to study the effect of temperature on bimetallic clusters. Two specific issues are addressed. The first issue concerns the use of different ensembles in simulation of finite systems. We make a semiquantitative comparison between the specific heat Cv and the root-mean-squared relative bond length fluctuation parameter δ of bimetallic clusters obtained in the present canonical ensemble simulations and those by the microcanonical ensemble. Systematic discongruity in the simulation results alludes to the inherent difference of the two ensembles for finite-sized systems. The second issue concerns the generally incomplete agreement in temperature dependences for Cv and δ. Here we make an analysis of the time evolution of the instantaneous relative bond length fluctuation rij, where the ith and jth are two atoms judiciously selected from the cluster. We give temporal evidence that the permutational isomer transition between ij-atoms in the bimetallic cluster which contributes to δ is due to these two atoms transiting to a higher-lying isomer state and this temporal behavior can be inferred from rij. The rij(t) therefore dictates the detail of the microscopic change in time and provides us with a means for understanding the incompatibility of δ and Cv
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