Theory of complex lattice Quasicontinuum and its application to ferroelectrics
Theory of complex lattice Quasicontinuum and its application to ferroelectrics
复制标题
复晶格准连续谱理论及其在铁电体中的应用
DOI：
--
复制
发表时间：
2005
期刊：
影响因子：
--
通讯作者：
O. Kowalewsky
中科院分区：
文献类型：
--
作者：
O. Kowalewsky
发展了复晶格准连续体理论，并将其应用于描述铁电现象。准连续统理论是一种多尺度理论，它结合原子论和连续统方法提供了对材料的统一描述。它提供了原子和连续体之间的无缝过渡，但材料的描述直接来自底层原子结构，仅在需要的地方使用计算昂贵的原子，在原子起源的现象的位置。
复晶格准连续体理论可以应用于由多种原子组成的复杂晶格晶体。它的一个亮点是尽可能单独和独立地处理每个组件晶格。准连续分量通过节点簇内的微观力耦合，使得非均匀晶格的复杂原子性成为描述的基础。
铁电体特别适合于准连续体理论的应用。铁电材料中的缺陷本质上是原子级的，但由于诱导的弹性场，它们对材料的影响是长期的。研究和模拟了钙钛矿型铁电体钛酸钡和钛酸铅的各种铁电现象。对于钛酸钡：180度畴壁结构和加载下的准静态裂纹。对于铅钛合金：180度畴壁结构和畴壁台阶。
畴壁的结果表明，畴壁的厚度是原子级小，几个晶格常数的顺序，这是在最近的从头计算分子动力学模拟协议，但我们也观察到长距离的影响所产生的存在下的壁。在裂纹加载过程中的样品的钛酸钡，我们观察到周围的裂纹尖端的极化变化与断裂韧性的增加的实验观察是一致的。畴壁台阶的准连续体研究给出了台阶平衡结构的原子观。
准连续体能够在缺陷和非均匀性周围以原子级精度模拟这些现象，并且还捕获样品中的长程效应的影响。这些研究也可以为更大规模的连续方法提供有价值的建模输入。
Complex lattice Quasicontinuum theory is developed and applied to the description of ferroelectric phenomena. Quasicontinuum theory is a multiscale theory that provides a unified description of materials by combining atomistic and continuum approaches. It provides a seamless transition between atomistics and continuum, but the description of the material is derived directly from the underlying atomic structure, using the computationally expensive atomistics only where needed, at the location of phenomena of atomistic origin.
Complex Lattice Quasicontinuum theory can be applied to complex lattice crystals consisting of many kinds of atoms. One highlight of it is treatment of each component lattice as separately and independently as possible. The component Quasicontinua are coupled through the microscopic forces within nodal clusters, making the complex atomistics of the heterogeneous lattice the basis of the description.
Ferroelectrics are especially suited to the application of Quasicontinuum theory. The nature of defects in ferroelectric materials is atomistic, but their influence over the material is long ranged due to induced elastic fields. Many different ferroelectric phenomena involving the perovskite ferroelectrics Barium Titanate and Lead Titanate are investigated and simulated. For Barium Titanate: the 180 degree domain wall structure and quasistatic crack under load. For Lead Titanate: the 180 degree domain wall structure and a domain wall step.
The results for the domain walls show that the domain wall thickness is atomistically small, of the order of few lattice constants, which is in agreement with recent ab initio molecular dynamics simulations, but we also observe long range effects resulting from the presence of the wall. During crack loading in the sample of Barium Titanate we observe polarization changes around the crack tip which are consistent with experimental observations of an increase of fracture toughness. The quasicontinuum study of a domain wall step gives an atomistical view into the equilibrium structure of the step.
Quasicontinuum is able to model these phenomena with atomistic precision around the defects and non-homogeneities, and also capture the influence of long-ranging effects in the samples. These studies could also give valuable modeling input for larger scale continuum approaches.