Quantifying the Likelihood of Structural Models through a Dynamically Enhanced Powder X‐Ray Diffraction Protocol

Abstract

Structurally characterizing new materials is tremendously challenging,especially when single crystal structures are hardly available which is often the case for covalent organic frameworks.Y et, knowledge of the atomic structure is key to establish structure-function relations and enable functional material design. Herein, an ew protocol is proposed to unambiguously predict the structure of poorly crystalline materials through al ikelihood ordering based on the X-ray diffraction (XRD) pattern. Keyo fthep rocedure is the broad set of structures generated from al imited number of building blocks and topologies,w hichi ss ubmitted to operando structural characterization. The dynamic averaging in the latter accounts for the operando conditions and inherent temporal character of experimental measurements,y ielding unparalleled agreement with experimental powder XRD patterns.T he proposed concept can hence unquestionably identify the structure of experimentally synthesized materials, ac rucial step to design next generation functional materials.

How the Layer Alignment in Two-Dimensional Nanoporous Covalent Organic Frameworks Impacts Its Electronic Properties

“…However, instead of optimizing the structural parameters, ab initio calculations were performed to obtain physically sound structural models. This gave rise to a collection of energetically favored stacking configurations at 0 K. However, as elaborated in our previous work, 58 a static approach to calculate the diffraction patterns introduces large discrepancies with the experiment due to an artificially decreased symmetry in the structures. As such, a dynamic approach was also considered, which accounted for the inherent temporal character of experimental measurements by considering an average PXRD pattern over the course of an MD simulation subjected to a finite pressure and temperature.…”

ReDD-COFFEE: a ready-to-use database of covalent organic framework structures and accurate force fields to enable high-throughput screenings

“…For each material, a static and dynamically averaged PXRD pattern is derived both with the QuickFF and UFF force elds, following our procedure outlined in ref. 50. Dynamical averaging at operando conditions is necessary for COFs to account for the inherent temporal character of experimental measurements.…”

“…Dynamical averaging at operando conditions is necessary for COFs to account for the inherent temporal character of experimental measurements. 50 In contrast to the static approach, during which the PXRD pattern is calculated for the optimized structure, the dynamic approach starts from an MD trajectory performed at operating conditions. The resulting PXRD pattern is an ensemble average of the pattern calculated for different snapshots from this trajectory.…”

“…In this work, we therefore present the ReDD-COFFEE database containing 268 687 COF structures, showcasing a great diversity in terms of geometric properties, linker cores, and linkages, and accompany each material with an ab initio derived force eld. Whereas such system-specic force elds have been developed earlier for a limited set of materials, [38][39][40][41][42][43][44][45][46][47][48][49][50] we have largely extended the scale of materials for which they are derived. Our ready-to-use database ensures molecular simulations can be directly started from the provided structures and force elds.…”

“…By deriving cluster force elds for the underlying building blocks, the number of required ab initio calculations is greatly reduced, while a high accuracy of the interatomic potential is maintained. [40][41][42][43][44][45][46][47][48][49][50] All COFs are assembled starting from a limited set of 279 SBUs, which are selected to result in a diverse database, as elaborated in Section 4.2. In contrast to other hypothetical databases, we have explicitly included a large number of linkage types in our database.…”