Sutter John P, Pittard James, Filik Jacob, Baron Alfred Q R
Diamond Light Source Ltd, Harwell Science and Innovation Campus, Chilton, Didcot, OX11 0DE, United Kingdom.
School of Physics, HH Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol, BS8 1TL, United Kingdom.
J Appl Crystallogr. 2022 Jul 28;55(Pt 4):1011-1028. doi: 10.1107/S1600576722005945. eCollection 2022 Aug 1.
The design of X-ray optics based on diffraction from crystals depends on the accurate calculation of the structure factors of their Bragg reflections over a wide range of temperatures. In general, the temperature dependence of the lattice parameters, the atomic positions and the atomic thermal vibrations is both anisotropic and nonlinear. Implemented here is a software package for precise and flexible calculation of structure factors for dynamical diffraction. α-Quartz is used as an example because it presents the challenges mentioned above and because it is being considered for use in high-resolution X-ray spectroscopy. The package is designed to be extended easily to other crystals by adding new material files, which are kept separate from the package's stable core. Python 3 was chosen as the language to allow the easy integration of this code into existing packages. The importance of a correct anisotropic treatment of the atomic thermal vibrations is demonstrated by comparison with an isotropic Debye model. Discrepancies between the two models can be as much as 5% for strong reflections and considerably larger (even to the level of 100%) for weak reflections. A script for finding Bragg reflections that backscatter X-rays of a given energy within a given temperature range is demonstrated. The package and example scripts are available on request. Also discussed, in detail, are the various conventions related to the proper description of chiral quartz.
基于晶体衍射的X射线光学器件设计依赖于在很宽温度范围内对其布拉格反射结构因子的精确计算。一般来说，晶格参数、原子位置和原子热振动的温度依赖性都是各向异性且非线性的。这里实现了一个用于精确灵活计算动态衍射结构因子的软件包。以α-石英为例，是因为它存在上述挑战，且正被考虑用于高分辨率X射线光谱学。该软件包设计为通过添加新材料文件可轻松扩展到其他晶体，这些文件与软件包的稳定核心分开保存。选择Python 3作为语言以便将此代码轻松集成到现有软件包中。通过与各向同性德拜模型比较，证明了对原子热振动进行正确各向异性处理的重要性。对于强反射，两种模型之间的差异可达5%，对于弱反射则差异更大（甚至达到100%）。展示了一个用于查找在给定温度范围内反向散射给定能量X射线的布拉格反射的脚本。该软件包和示例脚本可应要求提供。还详细讨论了与手性石英正确描述相关的各种惯例。
