Abstract AgCu nanoalloys are known to exhibit a size dependent transition to the chiral stacking from the anti-Mackay stacking. In the current work, the role of composition on the structural transitions between the anti-Mackay and the chiral stacking in AgCu nanoalloys has been studied computationally using a combination of global optimization searches and heating simulations. It is observed that in addition to the size, composition also affects the surface stacking in these nanoalloys. Further, results show that the nature of the recently reported thermally induced transition to the chiral stacking is strongly dependent on the Cu content in the AgCu nanoalloys. The amount of Cu in the nanoalloy affects both the transition temperature and the “sharpness” of the transition. By analyzing the frequencies of the vibrational modes calculated using the Harmonic Superposition Approximation (HSA), the thermal stability of the chiral stacking is attributed to the vibrational entropic contribution. Finally, the findings in the current work have been consolidated in the form of a size-composition map. By referring to this size-composition map, the preference for the chiral stacking can be understood for the nanoalloys belonging to the size window between the “magic” sized nanoalloys.

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关于 AgCu 纳米合金中反麦凯堆积、手性堆积及其热稳定性之间结构转变的性质

摘要 众所周知，AgCu 纳米合金表现出从反麦凯堆积到手性堆积的尺寸依赖性转变。在目前的工作中，使用全局优化搜索和加热模拟的组合，通过计算研究了成分对 AgCu 纳米合金中反麦凯和手性堆叠之间结构转变的作用。据观察，除了尺寸外，成分也会影响这些纳米合金的表面堆积。此外，结果表明，最近报道的向手性堆叠的热诱导转变的性质强烈依赖于 AgCu 纳米合金中的 Cu 含量。纳米合金中铜的含量影响转变温度和转变的“锐度”。通过分析使用谐波叠加近似 (HSA) 计算的振动模式的频率，手性堆叠的热稳定性归因于振动熵的贡献。最后，当前工作中的发现以尺寸组成图的形式进行了整合。通过参考此尺寸组成图，可以理解属于“神奇”尺寸纳米合金之间尺寸窗口的纳米合金对手性堆叠的偏好。