Chakraborty Somendra Nath, Chakravarty Charusita
Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India.
J Chem Phys. 2007 Jun 28;126(24):244512. doi: 10.1063/1.2743965.
The correlation between statistical properties of the energy landscape and the number of accessible configurational states, as measured by the exponential of the excess entropy (e(Se)), are studied in the case of a simple Lennard-Jones-type liquid in the neighborhood of the thermodynamic freezing transition. The excess entropy Se is defined as the difference between the entropy of the liquid and that of the ideal gas under identical temperature and pressure conditions and is estimated using the pair correlation contribution, S2. Landscape properties associated with three categories of configurations are considered: instantaneous configurations, inherent saddles, and inherent minima. Landscape properties studied include the energy and the key parameters of the Hessian eigenvalue distribution as well as the mean distances between instantaneous configurations and the corresponding inherent saddles and minima. The signatures of the thermodynamic freezing transition are clearest in the case of inherent structure properties which show, as a function of e(S2), a pronounced change in slope in the vicinity of the solid-liquid coexistence. The mean distance between instantaneous and saddle configurations also shows a similar change in slope when the system crosses from the stable to the supercooled regime. In the case of inherent saddles, the minimum eigenvalue acts as a similar indicator of the thermodynamic freezing transition but the average and maximum eigenvalues do not carry similar signatures. In the case of instantaneous configurations, a weak indicator of the thermodynamic freezing transition is seen in the behavior of the fraction of negative curvature directions as a function of the exponential of the excess entropy.
在热力学凝固转变附近的简单 Lennard-Jones 型液体的情况下，研究了能量景观的统计特性与可及构型状态数之间的相关性，该相关性由过量熵的指数（e(Se)）来衡量。过量熵 Se 被定义为在相同温度和压力条件下液体的熵与理想气体的熵之间的差值，并使用对关联贡献 S2 进行估计。考虑了与三类构型相关的景观特性：瞬时构型、固有鞍点和固有极小值。所研究的景观特性包括能量、海森矩阵特征值分布的关键参数，以及瞬时构型与相应固有鞍点和极小值之间的平均距离。在固有结构特性的情况下，热力学凝固转变的特征最为明显，其作为 e(S2) 的函数，在固液共存附近显示出斜率的显著变化。当系统从稳定区域过渡到过冷区域时，瞬时构型与鞍点构型之间的平均距离也显示出类似的斜率变化。在固有鞍点的情况下，最小特征值起到了类似的热力学凝固转变指标的作用，但平均特征值和最大特征值没有类似的特征。在瞬时构型的情况下，作为过量熵指数的函数，负曲率方向分数的行为中可以看到热力学凝固转变的一个弱指标。
