UCSI University, Cheras, Kuala Lumpur, Malaysia.
Acta Crystallogr C Struct Chem. 2021 Oct 1;77(Pt 10):586-590. doi: 10.1107/S2053229621009293. Epub 2021 Sep 22.
The present report lists selected publications on centrosymmetric compounds that manifest second harmonic generation responses in a laser, along with a few publications that dispute the laser outcomes. Two studies provide a plausible explanation for this apparent contradiction between second-order nonlinear susceptibility and inversion symmetry: the crystals are noncentrosymmetric and are twinned by inversion. If crystal structures of SHG-active compounds are presented in centrosymmetric settings, the authors of the publications may consider stipulating that the true space group is likely to be one of the noncentrosymmetric sub-space groups.
本报告列出了一些关于在激光中表现出二次谐波产生响应的中心对称化合物的选定出版物，以及一些对激光结果提出质疑的出版物。两项研究对二阶非线性极化率和反演对称性之间的这种明显矛盾提供了一个合理的解释：晶体是非中心对称的，并且通过反演进行了孪晶化。如果将具有二次谐波产生活性的化合物的晶体结构以中心对称的方式呈现，那么出版物的作者可能会考虑规定真实的空间群很可能是无中心对称子空间群之一。
