An enhanced set of displacement parameter restraints in CRYSTALS
An enhanced set of displacement parameter restraints in CRYSTALS
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DOI：
10.1107/s1600576718007100
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发表时间：
2018-08-01
影响因子：
6.1
通讯作者：
Cooper, Richard
中科院分区：
文献类型：
--
作者：
Parois, Pascal;Arnold, James;Cooper, Richard
晶体学约束广泛应用于小分子和大分子晶体结构的精细化。它们对于将额外的观测和信息引入到针对低质量或低分辨率数据（例如在高压下获得的数据）的结构细化中或者在无序或不稳定的细化中保留物理上有意义的参数值特别有用。然而，尽管各向异性位移参数（ADP）通常占结构分析中确定的总模型参数的一半以上，但对它们有用的约束相对较少，例如Hirshfeld刚性粘结约束、参数的直接等效和SHELXL RI GU型约束。相反，几何参数可能受到多种约束（例如绝对或相对距离、角度、平面性、手性体积和几何相似性）。本文介绍了在CRYSTALS [Parois，库珀& Thompson（2015），Chem. Cent. J. 9，30]中实施的一系列新ADP约束，以通过以各种方式约束局部定义的坐标系中椭球主轴的方向和大小来对ADP进行更多控制。使用这些新的ADP可以通过更高效、更快的设置约束来实现更逼真的模型和更好的用户体验。建议使用这些约束，以保持物理上有意义的位移参数之间的关系，在结构模型的刚体，旋转无序组和低完整性数据。
Crystallographic restraints are widely used during refinement of small-molecule and macromolecular crystal structures. They can be especially useful for introducing additional observations and information into structure refinements against low-quality or low-resolution data (e.g. data obtained at high pressure) or to retain physically meaningful parameter values in disordered or unstable refinements. However, despite the fact that the anisotropic displacement parameters (ADPs) often constitute more than half of the total model parameters determined in a structure analysis, there are relatively few useful restraints for them, examples being Hirshfeld rigid-bond restraints, direct equivalence of parameters and SHELXL RI GU-type restraints. Conversely, geometric parameters can be subject to a multitude of restraints (e.g. absolute or relative distance, angle, planarity, chiral volume, and geometric similarity). This article presents a series of new ADP restraints implemented in CRYSTALS [Parois, Cooper & Thompson (2015), Chem. Cent. J. 9, 30] to give more control over ADPs by restraining, in a variety of ways, the directions and magnitudes of the principal axes of the ellipsoids in locally defined coordinate systems. The use of these new ADPs results in more realistic models, as well as a better user experience, through restraints that are more efficient and faster to set up. The use of these restraints is recommended to preserve physically meaningful relationships between displacement parameters in a structural model for rigid bodies, rotationally disordered groups and low-completeness data.