Palomar Ricardo, Sesé Gemma
Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, Campus Nord-Mòdul B4, c/Jordi Girona 1-3, 08034 Barcelona, Spain.
J Chem Phys. 2008 Aug 14;129(6):064505. doi: 10.1063/1.2965878.
Spatial heterogeneities have been investigated in a supercooled system composed of diatomic molecules with an associated dipole moment by using the molecular dynamics simulation technique. Pair distribution functions of molecules with different mobilities have been evaluated, and it has been found that molecules belonging to the same dynamic domain are spatially correlated. Molecules with extremely large mobilities form larger clusters than those resulting from random statistics. These clusters are stringlike shaped. The mean cluster size displays a maximum at times between the ballistic and the diffusive regime, approximately at the end of the beta-relaxation zone. The value of this maximum increases upon cooling the system. An analogous profile has been observed for the characteristic cluster length when plotted against time. Agreement with Adam-Gibbs predictions has been encountered when considering these clusters as the basic dynamic units of the theory. For the extremely slow molecules, a cluster distribution has also been encountered. These clusters are smaller than the ones composed by fast molecules; they do not have a quasilinear geometry and no maximum is observed for their mean cluster size.
通过使用分子动力学模拟技术，在由具有相关偶极矩的双原子分子组成的过冷系统中研究了空间不均匀性。评估了具有不同迁移率的分子的对分布函数，发现属于同一动态域的分子在空间上是相关的。迁移率极大的分子形成的团簇比随机统计产生的团簇更大。这些团簇呈线状。平均团簇尺寸在弹道 regime 和扩散 regime 之间的时间出现最大值，大约在β弛豫区结束时。这个最大值在冷却系统时会增加。当将特征团簇长度与时间作图时，观察到类似的分布。当将这些团簇视为该理论的基本动态单元时，与亚当 - 吉布斯预测相符。对于极慢的分子，也遇到了团簇分布。这些团簇比由快速分子组成的团簇小；它们没有准线性几何形状，并且其平均团簇尺寸没有观察到最大值。
