Systematics of pure and doped 4He clusters.
Systematics of pure and doped 4He clusters.
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纯 4He 团簇和掺杂 4He 团簇的系统学。
DOI：
10.1103/physrevb.52.10405
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发表时间：
1995
期刊：
影响因子：
--
通讯作者：
Krotscheck
中科院分区：
文献类型：
--
作者：
Chin;Krotscheck
对{sup 4}He原子的纯团簇和掺杂团簇进行了优化变分计算，团簇大小为{ital N}=1000个粒子。对于小于或等于112个粒子的小簇大小，可以与现有的扩散蒙特卡罗结果进行比较，我们发现基态能量，相关性和结构函数非常一致。对于较大的星团，我们的基态能量平滑地向体积极限{负}7.2 K外推，表面能为0.272 K a {sup{负}2}。由此产生的基态密度显示出明显的振荡，证实了我们早先基于扩散蒙特卡罗研究的结论。目前对大型集群的研究使我们能够弥合有限系统和体积限制之间的差距。具体来说，我们展示了如何达到集体能量的体极限，以及如何在大液滴的动态结构函数的{ital S}波分量中再现体费曼谱。通过将高多极模式的集体激发能绘制为有效波数{ital k}={radical}{ital scrl}({ital scrl}+1)/{ital R}的函数，我们表明所得光谱可以直接与平面液体表面和薄膜的实验激发能进行比较。通过对{ital scrl}=50个部分波分量求和，我们发现完整的动态结构函数同时显示声子-光子和纹波子激发谱。在掺杂稀有气体原子或SF{sub 6}分子等杂质的氦液滴中，偶极子集体模式随着液滴尺寸的增加而变得不稳定，这强烈表明这些杂质在大液滴内离域。偶极子模式的激发函数和跃迁密度揭示了不稳定性的微观特征。（摘要节选）«少
Optimized variational calculations have been carried out for pure and doped clusters of {sup 4}He atoms up to a cluster size of {ital N}=1000 particles. For small cluster sizes with less than or equal to 112 particles, where comparisions with existing diffusion Monte Carlo results are possible, we find excellent agreement for the ground-state energy, correlation, and structure functions. For larger clusters our ground-state energies extrapolate smoothly toward a bulk limit of {minus}7.2 K with a surface energy of 0.272 K A{sup {minus}2}. The resulting ground-state densities show unmistakable oscillations, confirming our earlier conclusions based on diffusion Monte Carlo studies. The present study of large clusters allows us to bridge the gap between finite systems and the bulk limit. Specifically, we show how the bulk limit of collective energies is reached as well as how the bulk Feynman spectrum is reproduced in the {ital S}-wave component of the dynamic structure function in large droplets. By plotting the collective excitation energy of higher multipole modes as a function of an effective wave number {ital k}={radical}{ital scrl}({ital scrl}+1)/{ital R}, we show that the resulting spectrum can be directly compared with experimental excitation energies determined for plane liquid surfaces and films. By summingmore » up to {ital scrl}=50 partial wave components, we show that the full dynamic structure function simultaneously displays the phonon-roton and the ripplon excitation spectrum. In the case of helium droplets doped with impurities such as rare gas atoms or the SF{sub 6} molecule, we show that the dipole collective mode becomes unstable with increased droplet size, strongly indicating that these impurities are delocalized inside large droplets. The microscopic character of the instability is revealed in the excitation functions and transition densities of the dipole mode. (Abstract Truncated)« less