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arXiv 2106.08604cond-mat.stat-mechcond-mat.soft
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用密度泛函理论研究格子气中的液滴凝聚

Droplet condensation in the lattice gas with density functional theory

Manuel Maeritz, Martin Oettel

摘要:

从基本测度理论出发,将格子气(伊辛模型)的密度泛函应用于三维有限系统中的液滴状态问题。类似于以前的模拟研究,在增加系统中的平均密度$\barρ$后,发现液滴改变为圆柱体和平板的序列。由于晶格的离散性,在温度降低远离临界温度时,可以看到化学势$μ(\barρ)$的状态曲线中的附加效应(平板部分中的$μ(\barρ)$的振荡和圆柱部分中的$μ(\barρ)$的尖峰起伏以及液滴区域中的张力表面$R_s$的半径的波动行为)。在圆柱体和液滴区域中的这种行为与液体圆柱体和液滴表面处的冲刷分层过渡有关。表面张力$γ(R_s)$的大半径行为的分析给出了一个主要的贡献$\propto 1/R_s^2$,虽然$γ(R_s)$与半径依赖的托尔曼长度的渐近行为的一致性似乎表明在$γ(R_s)$中有一个弱的对数贡献$\propto \ln R_s/R_s^2$。该对数项的系数小于用场论方法导出的普适值。

英文摘要:

A density functional for the lattice gas (Ising model) from fundamental measure theory is applied to the problem of droplet states in three-dimensional, finite systems. Similar to previous simulation studies, the sequence of droplets changing to cylinders and to planar slabs is found upon increasing the average density $\barρ$ in the system. Owing to the discreteness of the lattice, additional effects in the state curve for the chemical potential $μ(\barρ)$ are seen upon lowering the temperature away from the critical temperature (oscillations in $μ(\barρ)$ in the slab portion and spiky undulations in $μ(\barρ)$ in the cylinder portion as well as an undulatory behavior of the radius of the surface of tension $R_s$ in the droplet region). This behavior in the cylinder and droplet region is related to washed-out layering transitions at the surface of liquid cylinders and droplets. The analysis of the large-radius behavior of the surface tension $γ(R_s)$ gave a dominant contribution $\propto 1/R_s^2$, although the consistency of $γ(R_s)$ with the asymptotic behavior of the radius-dependent Tolman length seems to suggest a weak logarithmic contribution $\propto \ln R_s/R_s^2$ in $γ(R_s)$. The coefficient of this logarithmic term is smaller than a universal value derived with field-theoretic methods.

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