دانلود رایگان مقاله روش برش کریستال برای مدل سازی کریستال در سلول شبیه سازی سه بعدی

Abstract

A Generalized Crystal-Cutting Method (GCCM) is developed that automates construction of three-dimensionally periodic simulation cells containing arbitrarily oriented single crystals and thin films, two-dimensionally (2D) infinite crystal–crystal homophase and heterophase interfaces, and nanostructures with intrinsic N-fold interfaces. The GCCM is based on a simple mathematical formalism that facilitates easy definition of constraints on cut crystal geometries. The method preserves the translational symmetry of all Bravais lattices and thus can be applied to any crystal described by such a lattice including complicated, low-symmetry molecular crystals. Implementations are presented with carefully articulated combinations of loop searches and constraints that drastically reduce computational complexity compared to simple loop searches. Orthorhombic representations of monoclinic and triclinic crystals found using the GCCM overcome some limitations in standard distributions of popular molecular dynamics software packages. Stability of grain boundaries in β-HMX was investigated using molecular dynamics and molecular statics simulations with 2D infinite crystal–crystal homophase interfaces created using the GCCM. The order of stabilities for the four grain boundaries studied is predicted to correlate with the relative prominence of particular crystal faces in lab-grown β-HMX crystals. We demonstrate how nanostructures can be constructed through simple constraints applied in the GCCM framework. Example GCCM constructions are shown that are relevant to some current problems in materials science, including shock sensitivity of explosives, layered electronic devices, and pharmaceuticals.

5. Conclusions

In this report we develop and implement a Generalized Crystal-Cutting Method (GCCM) for the systematic construction of three-dimensionally periodic simulation cells containing arbitrarily oriented single crystals and two-dimensionally infinite crystal–crystal interfaces. A simple mathematical formalism is used to conveniently express constraints on cut single-crystal geometries and is readily extended to specify constraints for constructing crystal–crystal homophase- and heterophase interfaces. The approach is generalized to include all Bravais lattices and so can be applied to complicated molecular crystals and materials that crystallize in low-symmetry systems. Search algorithms are implemented to find possible solutions for commensurate crystal cuts and an algorithm for populating the resulting simulation cells with constituent atoms and molecules is outlined. The GCCM is used to identify orthorhombic representations of a monoclinic crystal and some computational advantages of using an orthorhombic representation in molecular dynamics simulations are demonstrated. The GCCM is used to prepare simulation cells containing grain boundaries in monoclinic β-HMX crystals. The ranking order of their stabilities is predicted to correlate with the relative prominence of constituent crystal faces observed in an experimental study of β-HMX crystal habits and morphologies. The GCCM is applied to the construction of starting configurations for nanowires and icosahedral nanoparticles exhibiting five-fold twinned structures for subsequent molecular dynamics simulations. Additional example GCCM constructions are shown that could help address relevant materials science problems in areas including explosives, organic semiconductors, and pharmaceuticals.