Olson Isabel A, Shtukenberg Alexander G, Hakobyan Gagik, Rohl Andrew L, Raiteri Paolo, Ward Michael D, Kahr Bart
Department of Chemistry and Molecular Design Institute, New York University , New York City, New York 10003, United States.
Curtin Institute for Computation and Department of Chemistry, Curtin University , P.O. Box U1987, Perth, Western Australia 6845, Australia.
J Phys Chem Lett. 2016 Aug 18;7(16):3112-7. doi: 10.1021/acs.jpclett.6b01459. Epub 2016 Aug 1.
Spiral hillocks on n-alkane crystal surfaces were observed immediately after Frank recognized the importance of screw dislocations for crystal growth, yet their structures and energies in molecular crystals remain ill-defined. To illustrate the structural chemistry of screw dislocations that are responsible for plasticity in organic crystals and upon which the organic electronics and pharmaceutical industries depend, molecular dynamics was used to examine heterochiral dislocation pairs with Burgers vectors along [001] in n-hexane, n-octane, and n-decane crystals. The cores were anisotropic and elongated in the (110) slip plane, with significant local changes in molecular position, orientation, conformation, and energy. This detailed atomic level picture produced a distribution of strain consistent with linear elastic theory, giving confidence in the simulations. Dislocations with doubled Burgers vectors split into pairs with elementary displacements. These results suggest a pathway to understanding the mechanical properties and failure associated with elastic and plastic deformation in soft crystals.
在弗兰克认识到螺旋位错对晶体生长的重要性后，人们立即观察到正构烷烃晶体表面的螺旋小丘，然而它们在分子晶体中的结构和能量仍不明确。为了阐明导致有机晶体可塑性的螺旋位错的结构化学，而有机电子和制药行业依赖于这种可塑性，我们利用分子动力学研究了正己烷、正辛烷和正癸烷晶体中沿[001]方向具有伯格斯矢量的异手性位错对。位错核心是各向异性的，并且在(110)滑移面中伸长，分子位置、取向、构象和能量发生显著的局部变化。这一详细的原子水平图像产生了与线性弹性理论一致的应变分布，增强了对模拟的信心。具有双倍伯格斯矢量的位错分裂为具有基本位移的位错对。这些结果为理解软晶体中与弹性和塑性变形相关的力学性能和失效提供了一条途径。
