Two distinct approaches, that of energy and that of force, are adopted in quantum mechanics to get insights on chemical processes. In the second one, the net forces acting on the electrons and nuclei in a system (Ehrnefest and Hellmann–Feynman forces, respectively) are determined and a local version of the approach, in terms of force density fields rather than forces, has also been proposed for electrons. This is the path followed by Tsirelson & Stash (2020) in this issue of Acta Crystallographica Section B, to study for the first time the spatial distribution of the electronic forces of different nature acting in stable crystals. Interestingly, by relying on approximations taken from orbital‐free DFT, all components of the inner‐crystal force can be easily retrieved from multipole‐model refined experimental electron densities and their derivatives. No less important is that these calculations are becoming easily doable for any X‐ray density crystallographer thanks to a new version of the computer program WinXPRO, purposely developed in the study which is discussed in this commentary.

中文翻译：

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使用多极模型精细化的电子密度和无轨道DFT逼近看稳定晶体中的局部经典力和量子力

量子力学采用了两种截然不同的方法，即能量方法和力方法，以了解化学过程。在第二篇文章中，确定了作用在系统中电子和原子核上的净力（分别为Ehrnefest和Hellmann-Feynman力），并且已经确定了该方法的局部形式（根据力密度场而不是力）。建议用于电子。这是Tsirelson＆Stash（2020）在《晶体学报》 B期中遵循的方法首次研究了在稳定晶体中作用的不同性质电子力的空间分布。有趣的是，依靠无轨道DFT的近似值，可以轻松地从多极模型精制的实验电子密度及其导数中检索出内部晶体力的所有分量。同样重要的是，得益于专门在研究中开发的计算机程序WinXPRO的新版本，这些计算对于任何X射线密度晶体学专家而言都变得容易进行，本评论对此进行了讨论。