基于分子晶体序参数与K-means聚类的 TNT晶型转化有限温度弦研

To reveal the molecular mechanism of the rare events of polymorphic transformation for explosive, two types of order parameter were constructed based on the bond distance (i.e., intermolecular distance), bond orientation, and molecular orientation.The enhanced sampling of the order parameter was performed by using K-means clustering algorithm based on Euclidean distance and weighted density.As a result, the conventional finite temperature string (FTS) method is improved for rare events based on molecular crystal order parameter and enhanced K-means clustering sampling, leading to a fast convergent of the free energy of the polymorphic transformation.By applying this method to investigate the polymorphic transformation of TNT, the "dimensional explosion" of the order parameter of molecular crystal is avoided, and the potential of mean force is obtained.The results not only verify the effectiveness of the FTS method based on molecular crystal order parameters and K-means clustering in the investigation of the polymorphic transformation for explosive, but also reveal the polymorphic transformation process between TNT(O) and TNT(M), namely surface-mediated, local initiation, and multi-nucleus asynchronous growth.