Symmetry-general least-squares extraction of elastic data for strained materials from ab initio calculations of stress -: art. no. 104104
Symmetry-general least-squares extraction of elastic data for strained materials from ab initio calculations of stress -: art. no. 104104
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DOI：
10.1103/physrevb.65.104104
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发表时间：
2002-03-01
影响因子：
3.7
通讯作者：
Saxe, P
中科院分区：
文献类型：
--
作者：
Le Page, Y;Saxe, P
本文报道了一种用于最小二乘的对称一般方法，因此可以精确地提取应变材料的弹性系数。它分析应力从头计算适当选择应变。这个问题，它的实现，以及它的解决策略都与我们去年发表的之前的能量-应变方法有根本的不同，但是正常的方程被证明是适用于相同的约束方案，这使得两种方法都是对称的。详细介绍了控制自动选择适当应变模型及其笛卡尔系统的对称性考虑。讨论并实现了对一般应力下材料的扩展。采用VASP进行应力从头计算。全面的例子包括三斜材料（蓝晶石）和零压力下具有一系列对称性的简单材料，静水压力下的MgO，[001]单轴应变下的Ti4As3和[001]单轴应力下的Si。MgO的情况与最近的实验工作一致，包括弹性系数及其一阶和二阶导数。Si的弹性系数曲线显示，33柔度系数逐渐增大，导致材料在-11.7 GPa时坍塌，而实验值为-12.0 GPa。用两种近似[局部密度（LDA）、广义梯度（GGA）]、两种方法（应力应变和能量应变）解释Be的结果两种潜在类型（投影仪增强波和超软）和两个量子引擎（VASP和ORESTES）揭示了用于弹性计算的细胞数据的最大重要性和其他因素的次要重要性。对于松弛单元数据的刚度，差异主要源于LDA对x射线单元数据的残余压应力的相当大的高估，导致松弛单元较小，因此对角刚度系数值较大。这里描述的方法具有对称的通用性，可以创建健壮的用户界面，无缝地从数据库搜索到弹性系数的打印输出。有了它，即使是非专业用户也可以可靠地从CRYSTMET(R)和ICSD(R)结构数据库中的相应条目（即已知晶体结构的所有纯相无机材料）中以简单的点击方式生成与技术相关的结果，就像这里讨论的那样。Ti4As3的案例揭示了，在第一批属性，刚度，顺应性和各向同性属性上，可以从中得出，目前的现实是使用从头算软件挖掘晶体结构数据库，以获取以前从未测量过的技术属性。目前正在朝着这个方向进一步发展。
A symmetry-general approach for the least-squares, therefore precise, extraction of elastic coefficients for strained materials is reported. It analyzes stresses calculated ab initio for properly selected strains. The problem, its implementation, and its solution strategy all differ radically from a previous energy-strain approach that we published last year, but the normal equations turn out to be amenable to the same constrainment scheme that makes both approaches symmetry general. The symmetry considerations governing the automated selection of appropriately strained models and their Cartesian systems are detailed. The extension to materials under general stress is discussed and implemented. VASP was used for ab initio calculation of stresses. A comprehensive range of examples includes a triclinic material (kyanite) and simple materials with a range of symmetries at zero pressure, MgO under hydrostatic pressure, Ti4As3 under [001] uniaxial strain, and Si under [001] uniaxial stress. The MgO case agrees with recent experimental work including elastic coefficients as well as their first and second derivatives. The curves of elastic coefficients for Si show a gradual increase in the 33 compliance coefficient, leading to a collapse of the material at -11.7 GPa, compared with -12.0 GPa experimentally. Interpretation of results for Be using two approximations [local density (LDA), generalized gradient (GGA)], two approaches (stress strain and energy strain!, two potential types (projector augmented wave and ultrasoft), and two quantum engines (VASP and ORESTES) expose the utmost importance of the cell data used for the elastic calculations and the lesser importance of the other factors. For stiffness at relaxed cell data, differences are shown to originate mostly in the considerable overestimation of the residual compressive stresses at x-ray cell data by LDA, resulting in a smaller relaxed cell, thus larger values for diagonal stiffness coefficients. The symmetry generality of the approach described here enabled the creation of a robust user interface going seamlessly from the database search to the printout of the elastic coefficients. With it, even nonspecialist users can reliably produce technologically relevant results like those discussed here in a simple point-and-click fashion from corresponding entries in the CRYSTMET(R) and ICSD(R) structure databases, i.e., for all pure-phase nonorganic materials with known crystal structure. The case of Ti4As3 exposes, on a first cluster of properties, stiffness, compliance, and the isotropic properties that can be derived from them, the current reality of mining crystal structure databases with ab initio software for technological properties that were never measured before. Further developments in that direction are currently underway.