Jain Tushar S, de Pablo Juan J
Department of Chemical and Biological Engineering, University of Wisconsin-Madison, 53706, USA.
J Chem Phys. 2005 May 1;122(17):174515. doi: 10.1063/1.1888505.
We have conducted detailed Monte Carlo and molecular dynamics simulations of a model glass forming polymeric system near its apparent glass transition temperature. We have characterized the local structure of the glass using a Voronoi-Delaunay analysis of local particle arrangements. After a perturbative face elimination, we find that a significant fraction of Voronoi polyhedra consist of 12 pentagonal faces, a sign of icosahedral ordering. Further, we have identified metabasins of particle vibrations on the potential energy landscape on the basis of persistence of particle positions and neighbors over a simulated trajectory. We find that the residence times for vibrations are correlated with a particular Voronoi volume and number of neighbors of a particle; the largest metabasins correspond to particles whose average Voronoi volume is close to the value expected on the basis of the density, and whose approximate number of neighbors is close to 12. The local distortion around a particle, measured in terms of the tetrahedricity of the Delaunay simplices, reveals that the particles with a higher degree of local distortion are likely to transition faster to a neighboring metabasin. In addition to the transition between metabasins, we have also examined the influence of vibrations at inherent structures (IS) on the local structure, and find that the the low frequency modes at the IS exhibit the greatest curvature with respect to the local structure. We believe that these results establish an important connection between the local structure of glass formers and the activated dynamics, thereby providing insights into the origins of dynamic heterogeneities.
我们对一种模型玻璃形成聚合物体系在其表观玻璃化转变温度附近进行了详细的蒙特卡罗和分子动力学模拟。我们使用局部粒子排列的Voronoi-Delaunay分析来表征玻璃的局部结构。经过微扰面消除后，我们发现很大一部分Voronoi多面体由12个五边形面组成，这是二十面体有序的标志。此外，我们基于模拟轨迹上粒子位置和邻居的持续性，在势能面上确定了粒子振动的亚稳态盆地。我们发现振动的停留时间与粒子的特定Voronoi体积和邻居数量相关；最大的亚稳态盆地对应于平均Voronoi体积接近基于密度预期值且邻居数量近似为12的粒子。以Delaunay单形的四面体性来衡量，粒子周围的局部畸变表明，局部畸变程度较高的粒子可能更快地转变到相邻的亚稳态盆地。除了亚稳态盆地之间的转变，我们还研究了固有结构（IS）处的振动对局部结构的影响，发现IS处的低频模式相对于局部结构表现出最大的曲率。我们相信这些结果在玻璃形成体的局部结构与活化动力学之间建立了重要联系，从而为动态非均匀性的起源提供了见解。
