Dynamics and configurational entropy in the Lewis-Wahnstrom model for supercooled orthoterphenyl
Dynamics and configurational entropy in the Lewis-Wahnstrom model for supercooled orthoterphenyl
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DOI：
10.1103/physreve.65.041205
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发表时间：
2002-04-01
影响因子：
2.4
通讯作者：
Tartaglia, P
中科院分区：
文献类型：
--
作者：
Mossa, S;La Nave, E;Tartaglia, P
研究了脆性玻璃形成液体邻三联苯的刚性模型的热力学和动力学性质。这个模型是由刘易斯和瓦恩斯特罗姆在1993年提出的，它将每个苯环坍缩成一个相互作用位点;分子间的位点-位点相互作用由伦纳-琼斯势描述，其参数被选择来再现邻三联苯分子的一些整体性质。在很宽的密度和温度范围内考虑了N=343分子的系统，这样长的轨迹允许我们在低于模式耦合温度Tc的温度下平衡系统，在该温度下扩散常数达到10（-10）cm（2）/cm（2）量级的值。s，从而以显著的方式对整个温度范围内的势能景观进行采样。在固有的结构热力学形式主义的工作，我们提出的结果的温度和密度依赖的数量，深度和形状的盆地的势能面。我们估计的总熵的热力学积分从理想的非相互作用的气体状态和振动熵近似的盆地自由能与6 N-3谐振子的自由能。我们评估的熵作为这两个贡献之间的差异的配置部分。我们研究了系统的化学性质和动力学性质之间的联系。我们确认的温度依赖性的构型熵和扩散常数，以及逆的特征结构弛豫时间，是强连接在过冷状态，我们证明，这种连接是很好地表示的亚当-吉布斯关系，说明logD和数量1/TSc之间的线性关系。这种关系被发现保持在临界温度T-C以上和以下-如先前发现的情况下，二氧化硅-支持的假设，即连接的数量之间存在的盆地和势能面的连接性。
We study thermodynamic and dynamic properties of a rigid model of the fragile glass-forming liquid orthoterphenyl. This model, introduced by Lewis and Wahnstrom in 1993, collapses each phenyl ring to a single interaction site; the intermolecular site-site interactions are described by the Lennard-Jones potential whose parameters have been selected to reproduce some bulk properties of the orthoterphenyl molecule. A system of N=343 molecules is considered in a wide range of densities and temperatures, reaching simulation times up to 1 mus. Such long trajectories allow us to equilibrate the system at temperatures below the mode coupling temperature T-c at which the diffusion constant reaches values of order 10(-10) cm(2)/s and thereby to sample in a significant way the potential energy landscape in the entire temperature range. Working within the inherent structures thermodynamic formalism, we present results for the temperature and density dependence of the number, depth and shape of the basins of the potential energy surface. We evaluate the total entropy of the system by thermodynamic integration from the ideal-noninteracting-gas state and the vibrational entropy approximating the basin free energy with the free energy of 6N-3 harmonic oscillators. We evaluate the configurational part of the entropy as a difference between these two contributions. We study the connection between thermodynamical and dynamical properties of the system. We confirm that the temperature dependence of the configurational entropy and of the diffusion constant, as well as the inverse of the characteristic structural relaxation time, are strongly connected in supercooled states; we demonstrate that this connection is well represented by the Adam-Gibbs relation, stating a linear relation between logD and the quantity 1/TSc. This relation is found to hold both above and below the critical temperature T-c-as previously found in the case of silica-supporting the hypothesis that a connection exists between the number of basins and the connectivity properties of the potential energy surface.