Study On Predicting Morphology Of Organic Micro-/Nano-Crystals

Understanding the process of molecular self-assembly and predicting the structure/morphology of organic micro-/nano-crystals have always been challenging subjects in crystallography,nano-science and materials science.This paper aims to predict organic crystal morphologies under non-equilibrium thermodynamic process through molecular structure files.The theoretical basis of this paper is PBC theory and non-equilibrium thermodynamics.Key technologies include virtual screening,molecule dynamics and first-principle（DFT）.The research object is fluorenyl molecules（mainly spirofluorene molecules）and the research content is as follows:（1）The relationships between the patterns of molecular aggregation and the structural dimensions of organic micro-/nano-crystals were studied.Firstly,two aggregation modes（step&chain）were observed by calculating and analyzing the intermolecular non-covalent interactions.Secondly,it is found that the step mode is easy to form 2D micro-/nano-structures,while chain mode is easy to form3D/1D micro-/nano-structures by using statistical analysis.（2）Space group prediction and organic crystal structure simulation were investigated.In this paper,using molecule dynamics to simulate organic crystal structures is facilitated by predicting space group parameter with virtual screening.During the research,the Morgan model emphasizing two-dimensional global feature,the MACCS model emphasizing two-dimensional substructural feature,and the USR model emphasizing three-dimensional spatial structural feature were established to predict space groups.The predicting results show that the USR model exhibits the highest accuracy of all models（50%）,but the Morgan model presents the highest hit rate of all models（90%）.Due to the lacking-data set of spirofluorene molecules,this paper proposes to cross-refer the results of the USR model and the Morgan model to ensure the accuracy of prediction.The accuracy of simulating organic crystal structure by molecule dynamics is 40%when the predicted space group is consistent with experiment.（3）A method for predicting the morphologies of organic crystals under non-equilibrium thermodynamic process is proposed.The process is as follows:firstly,exposed surfaces with Miller indexes of organic micro-/nano-crystal are confirmed by PBC theory.Secondly,calculated weak interactions in each direction by using Gaussian,were used to calculate the energy required for each crystallographic plane to grow along with the relative growth rates(R_hkl)under non-equilibrium thermodynamic process.Finally,entering Mille index,R_hkl,point group and lattice parameters into Win XMorph to simulate the morphology of organic micro-/nano-crystals.The simulated results show that the method proposed in this paper is more accurate than BFDH,Equilibrium morphology and Growth morphology in predicting the morphology of organic crystal under non-equilibrium thermodynamic process.