Structure and Phase Transition in Systems of Large Molecules

大分子系统的结构和相变

• 批准号: 10640360
• 负责人: HASEGAWA Masayuki
• 金额: $ 1.6万
• 依托单位: Iwate University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 1998
• 资助国家: 日本
• 起止时间: 1998 至 2000
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-10640360/
• 关键词: Fulleren; Large Molecule; Intermolecular Potential; Equation of State; Orientational Phase Transition; Computer Simulation; Monte Carlo Method; C_<60>; 固相-液相転移; 気相-液相転移; 計算機実験; 液相-固相転移; モンテカルロシミュレーション

In systems with sufficiently short-ranged attractive potentials the sublimation line passes above the liquid-vapor critical temperature and the liquid phase no more exists as a thermodynamically stable state. The isostructual solid-solid transition also occurs for systems with further short-ranged potentials. In the present study systematic investigation is made for these unusual phase behaviors using a thermodynamic perturbation theory and Monte Carlo simulation method. Main focus is put on the fulleren C_<60> and it is found that this substance has a stable liquid phase only in the very nallow range of temperature. However, the temperature concerned is very high (〜2000K) to be confirmed experimentally. The isostuctural solid-solid transition is expected to occur, at least in principle, in colloids.The second subject is C_<60> solid which is a typical plastic solid and shows the orientational order-disorder transition, which is a manifestation of small anisotropy of C_<60> molecules. We proposed a simple model which provides a unified picture for the equaution of state and orientational transition under pressure. This model consists of the effective intermolecular potentials constructed for both phases using the existing first-principle electronic structure calculations for C_<60> solid.The third subject in the present study is concerned with limitation of the computer simulation method used for the phase transition and it is found that the phase boundaries determined by the visual molecular configurations in computer simulations are quite different from those obtained by the thermodynamic condition of coexistence. We paid a special attention to the high-temperature phase diagram of C_<60> and found that some of the previous simulations based on the visual method are wrong.

在足够短的吸引力电位的系统中，升华线通过液体蒸气临界温度，而液相不再存在作为热力学稳定的状态。具有进一步短势势的系统也会发生等值结构固体过渡。在本研究中，使用热力学扰动理论和蒙特卡洛模拟方法对这些异常的相行为进行了系统研究。主要重点放在富勒素C_ <60>上，发现该物质仅在非常狭窄的温度范围内具有稳定的液相。但是，相关的温度非常高（〜2000K），可以通过实验确认。等静脉固体固定转变至少在原则上是在胶体中发生。第二个受试者是C_ <60>固体，这是典型的塑料固体，并显示了定向阶的阶端转变，这是C_ <60>分子的小各向异性的表现。我们提出了一个简单的模型，该模型为在压力下的状态和定向过渡提供了统一的图片。该模型由使用C_ <60>实心的现有第一原理电子结构计算构建的有效分子间电位组成。本研究中的第三个受试者与用于相变的计算机模拟方法的限制有关，并且发现由计算机模拟在这些cocect cocect coce coc的情况下，由计算机模拟确定的相位边界完全不同。我们特别注意C_ <60>的高温相图，发现基于视觉方法的一些先前模拟是错误的。

项目成果

Orie Umiguchi: "Simple model for the equation of state and orientational order-disorder transition of C_<60> solid under pressure" Journal of the Physical Society of Japan. 68・2. 508-514 (1999)

Orie Umiguchi：“压力下 C_<60> 固体的状态方程和取向有序-无序转变的简单模型”日本物理学会杂志 68・2（1999）。

M.Hasegaw: "Can the visual molecular configuration in computer simulations locate solid-fluid phase boundaries? The case of C_<60>"Journal of Chemical Physics. 113(10). 4315-4319 (2000)

M.Hasegaw：“计算机模拟中的可视化分子构型能否定位固-液相边界？以C_<60>为例”《化学物理杂志》。

R.Sahara: "Body-centered-cubic lattice model with many-body interactions representing melting transition in Si"Journal of Chemical Physics. 110(119). 9608-9617 (1999)

R.Sahara：“具有代表硅熔化转变的多体相互作用的体心立方晶格模型”化学物理杂志。

長谷川正之: "高温におけるC_<60>の相図:計算機実験の限界"超微粒子とクラスター懇談会論文集. 4. 149-152 (2000)

Masayuki Hasekawa：“高温下 C_<60> 的相图：计算机实验的限制”超细颗粒和团簇会议论文集 4. 149-152 (2000)。

M.Hasegawa: "Monte Carlo simulation study for the high-temperature phase diagram of model C_<60> molecules"Journal of Chemical Physics. 111・13. 5559-5963 (1999)

M.Hasekawa：“模型C_<60>分子的高温相图的蒙特卡罗模拟研究”化学物理杂志111・13（1999）。