Chodkiewicz Michał Leszek, Olech Barbara, Jha Kunal Kumar, Dominiak Paulina Maria, Woźniak Krzysztof
Biological and Chemical Research Centre, Department of Chemistry, University of Warsaw, Żwirki i Wigury 101, Warszawa, Warszawa 02-089, Poland.
Centre of New Technologies, University of Warsaw, S. Banacha 2c, Warsaw 02-097, Poland.
IUCrJ. 2024 Sep 1;11(Pt 5):730-736. doi: 10.1107/S2052252524006808.
Reaching beyond the commonly used spherical atomic electron density model allows one to greatly improve the accuracy of hydrogen atom structural parameters derived from X-ray data. However, the effects of atomic asphericity are less explored for electron diffraction data. In this work, Hirshfeld atom refinement (HAR), a method that uses an accurate description of electron density by quantum mechanical calculation for a system of interest, was applied for the first time to the kinematical refinement of electron diffraction data. This approach was applied here to derive the structure of ordinary hexagonal ice (I). The effect of introducing HAR is much less noticeable than in the case of X-ray refinement and it is largely overshadowed by dynamical scattering effects. It led to only a slight change in the O-H bond lengths (shortening by 0.01 Å) compared with the independent atom model (IAM). The average absolute differences in O-H bond lengths between the kinematical refinements and the reference neutron structure were much larger: 0.044 for IAM and 0.046 Å for HAR. The refinement results changed considerably when dynamical scattering effects were modelled - with extinction correction or with dynamical refinement. The latter led to an improvement of the O-H bond length accuracy to 0.021 Å on average (with IAM refinement). Though there is a potential for deriving more accurate structures using HAR for electron diffraction, modelling of dynamical scattering effects seems to be a necessary step to achieve this. However, at present there is no software to support both HAR and dynamical refinement.
超越常用的球形原子电子密度模型能够极大地提高从X射线数据推导得到的氢原子结构参数的准确性。然而，对于电子衍射数据，原子非球形效应的研究较少。在这项工作中，首次将Hirshfeld原子精修（HAR）方法应用于电子衍射数据的运动学精修，该方法通过对感兴趣的系统进行量子力学计算来精确描述电子密度。此方法在此处用于推导普通六方冰（I）的结构。引入HAR的效果比X射线精修的情况要小得多，并且在很大程度上被动态散射效应所掩盖。与独立原子模型（IAM）相比，它仅导致O - H键长有轻微变化（缩短0.01 Å）。运动学精修与参考中子结构之间O - H键长的平均绝对差值要大得多：IAM为0.044 Å，HAR为0.046 Å。当对动态散射效应进行建模时，无论是消光校正还是动态精修，精修结果都会有很大变化。后者使得O - H键长精度平均提高到0.021 Å（采用IAM精修）。尽管使用HAR对电子衍射推导更精确结构具有潜力，但对动态散射效应进行建模似乎是实现这一目标的必要步骤。然而，目前尚无支持HAR和动态精修的软件。
