Reimers Jeffrey R, Tawfik Sherif Abdulkader, Ford Michael J
International Centre for Quantum and Molecular Structures , School of Physics , Shanghai University , Shanghai 200444 , China . Email:
School of Mathematical and Physical Sciences , University of Technology Sydney , Ultimo , New South Wales 2007 , Australia . Email:
Chem Sci. 2018 Sep 17;9(39):7620-7627. doi: 10.1039/c8sc01274a. eCollection 2018 Oct 21.
We show how van der Waals (vdW) forces outcompete covalent and ionic forces to control ferroelectric ordering in CuInPS nanoflakes as well as in CuInPS and CuBiPSe crystals. While the self-assembly of these 2D layered materials is clearly controlled by vdW effects, this result indicates that the internal layer structure is also similarly controlled. Using up to 14 first-principles computational methods, we predict that the bilayers of both materials should be antiferroelectric. However, antiferroelectric nanoflakes and bulk materials are shown to embody two fundamentally different types of inter-layer interactions, with vdW forces strongly favouring one and strongly disfavouring the other compared to ferroelectric ordering. Strong specific vdW interactions involving the Cu atoms control this effect. Thickness-dependent significant cancellation of these two large opposing vdW contributions results in a small net effect that interacts with weak ionic contributions to control ferroelectric ordering.
我们展示了范德华（vdW）力如何胜过共价键和离子键力，从而控制CuInPS纳米薄片以及CuInPS和CuBiPSe晶体中的铁电有序性。虽然这些二维层状材料的自组装显然受vdW效应控制，但这一结果表明其内层结构也受到类似的控制。我们使用多达14种第一性原理计算方法预测，这两种材料的双层结构都应为反铁电体。然而，反铁电纳米薄片和块状材料体现出两种根本不同类型的层间相互作用，与铁电有序性相比，vdW力强烈偏向其中一种，而强烈不利于另一种。涉及铜原子的强特定vdW相互作用控制了这一效应。这两个大的相反vdW贡献随厚度的显著抵消导致一个小的净效应，该净效应与弱离子贡献相互作用以控制铁电有序性。
