AIRBED: A Simplified Density Functional Theory Model for Physisorption on Surfaces.

Stephen E Mason,Nicholas A Besley,Peter H Beton

doi:10.1021/acs.jctc.9b00576

Stephen E Mason, Nicholas A Besley + Show 1 more

Open Access

https://doi.org/10.1021/acs.jctc.9b00576

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Abstract

Dispersion interactions are commonly included in density functional theory (DFT) calculations through the addition of an empirical correction. In this study, a modification is made to the damping function in DFT-D2 calculations to describe repulsion at small internuclear distances. The resulting Atomic Interactions Represented By Empirical Dispersion (AIRBED) approach is used to model the physisorption of molecules on surfaces such as graphene and hexagonal boron nitride, where the constituent atoms of the surface are no longer required to be included explicitly in the density functional theory calculation but are represented by a point charge to capture electrostatic effects. It is shown that this model can reproduce the structures predicted by full DFT-D2 calculations to a high degree of accuracy. The significant reduction in computational cost allows much larger systems to be studied, including molecular arrays on surfaces and sandwich complexes involving organic molecules between two surface layers.

Highlights

The study of 2-dimensional (2D) arrays of organic molecules on surfaces is an increasingly important area of research owing to their potential applications in a range of fields including electronic and optoelectronic devices.[1,2,3,4] Understanding the interactions that underpin the organisation of these arrays is key to realising their potential
We focus on two aspects of the structures, firstly, the height of the molecule above the surface and the root mean square deviation (RMSD) between the structures of the adsorbed molecules
The density functional theory (DFT)-D2 calculations predict that the molecules are further from the surface of graphene compared with hexagonal boron nitride (hBN), and this trend is replicated by the Atomic Interactions Represented By Empirical Dispersion (AIRBED) calculations

Summary

Introduction

The study of 2-dimensional (2D) arrays of organic molecules on surfaces is an increasingly important area of research owing to their potential applications in a range of fields including electronic and optoelectronic devices.[1,2,3,4] Understanding the interactions that underpin the organisation of these arrays is key to realising their potential. These interactions can include hydrogen bonding, covalent bonding, dispersion forces and metal coordination, which may all have a significant role in the structure of the array.[5,6,7,8] One area of particular focus is the study of organic arrays on surfaces such as graphene and hexagonal boron nitride (hBN). These arrays can be imaged using scanning tunnelling microscopy and atomic force microscopy, which can provide high-resolution images of 2D molecular and supramolecular organization under ultra-high-vacuum conditions and at atmospheric pressure.[9,10,11,12,13] When adsorbed on insulating surfaces, the fluorescence of the adsorbed molecular layers can be measured providing a direct link to the optoelectronic properties of the arrays.[14,15,16,17,18,19,20]

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