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arXiv 1104.3426cond-mat.soft
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高密度高斯核模型的热力学和结构性质

Thermodynamics and Structural Properties of the High Density Gaussian Core Model

Atsushi Ikeda, Kunimasa Miyazaki

摘要:

我们数值研究了单组分高斯核模型(GCM)在非常高密度下的热力学和结构性质。固体-流体相边界被仔细地确定。我们发现,冻结温度和融化温度的密度依赖性都服从渐近关系$\log T_f$,$\log T_m \propto -ρ^{2/3}$,其中$ρ$是数密度,这与Stillinger猜想是一致的.热力学量,如能量和压力和结构功能,如静态结构因子也研究了在流体相的相边界以上的温度范围宽。我们比较的数值结果与预测的液体理论与无规相近似(RPA)。在高温下,结果与RPA在广泛的密度范围内几乎完全一致,正如先前的研究所示。在相边界线附近的低温区,RPA虽然不能描述粒子间距离尺度下的结构因子和径向分布函数,但能成功地预测它们在更短尺度下的行为。RPA还几乎完美地预测热力学量,例如能量、压力和热膨胀系数变为负值时的温度。RPA预测热力学量的惊人能力,即使在高密度和低温度下被理解的解耦的长度尺度决定热力学量从粒子间的距离,占主导地位的静态结构因子的峰值结构,由于高斯核势的柔软性。

英文摘要:

We numerically study thermodynamic and structural properties of the one-component Gaussian core model (GCM) at very high densities. The solid-fluid phase boundary is carefully determined. We find that the density dependence of both the freezing and melting temperatures obey the asymptotic relation, $\log T_f$, $\log T_m \propto -ρ^{2/3}$, where $ρ$ is the number density, which is consistent with Stillinger's conjecture. Thermodynamic quantities such as the energy and pressure and the structural functions such as the static structure factor are also investigated in the fluid phase for a wide range of temperature above the phase boundary. We compare the numerical results with the prediction of the liquid theory with the random phase approximation (RPA). At high temperatures, the results are in almost perfect agreement with RPA for a wide range of density, as it has been already shown in the previous studies. In the low temperature regime close to the phase boundary line, although RPA fails to describe the structure factors and the radial distribution functions at the length scales of the interparticle distance, it successfully predicts their behaviors at shorter length scales. RPA also predicts thermodynamic quantities such as the energy, pressure, and the temperature at which the thermal expansion coefficient becomes negative, almost perfectly. Striking ability of RPA to predict thermodynamic quantities even at high densities and low temperatures is understood in terms of the decoupling of the length scales which dictate thermodynamic quantities from the interparticle distance which dominates the peak structures of the static structure factor due to the softness of the Gaussian core potential.

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