Towards coarse-grained elasticity of single-layer Covalent Organic Frameworks

TL;DR

This paper develops computational models to describe the elastic properties of single-layer covalent organic frameworks, linking molecular force constants to macroscopic elasticity, and validates the models with defect deformation energy calculations.

Contribution

It introduces two coarse-grained elastic models for 2D COFs based on molecular force constants, enabling efficient prediction of elastic behavior.

Findings

Good agreement between coarse-grained models and detailed calculations for defect deformation energy.

Models successfully connect molecular linker properties to macroscopic elastic constants.

Approximately 40 COFs analyzed for elastic properties.

Abstract

Two-dimensional covalent organic frameworks (2D COFs) are an interesting class of 2D materials since their reticular synthesis allows the tailored design of structures and functionalities. For many of their applications the mechanical stability and performance is an important aspect. Here, we use a computational approach involving a density-functional based tight-binding method to calculate the in-plane elastic properties of about 40 COFs with a honeycomb lattice. Based on those calculations, we develop two coarse-grained descriptions: one based on a spring network and the second using a network of elastic beams. The models allow us to connect the COF force constants to the molecular force constants of the linker molecules and thus enable an efficient description of elastic deformations. To illustrate this aspect, we calculate the deformation energy of different COFs containing the equivalent of a Stone-Wales defect and find very good agreement with the coarse-grained description.