Energy level alignment at molecule-metal interfaces from an optimally tuned range-separated hybrid functional

Zhen-Fei Liu,Sivan Refaely-Abramson,Jeffrey B Neaton,David A Egger,Leeor Kronik

doi:10.1063/1.4975321

Zhen-Fei Liu, Sivan Refaely-Abramson + Show 3 more

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https://doi.org/10.1063/1.4975321

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Abstract

The alignment of the frontier orbital energies of an adsorbed molecule with the substrate Fermi level at metal-organic interfaces is a fundamental observable of significant practical importance in nanoscience and beyond. Typical density functional theory calculations, especially those using local and semi-local functionals, often underestimate level alignment leading to inaccurate electronic structure and charge transport properties. In this work, we develop a new fully self-consistent predictive scheme to accurately compute level alignment at certain classes of complex heterogeneous molecule-metal interfaces based on optimally tuned range-separated hybrid functionals. Starting from a highly accurate description of the gas-phase electronic structure, our method by construction captures important nonlocal surface polarization effects via tuning of the long-range screened exchange in a range-separated hybrid in a non-empirical and system-specific manner. We implement this functional in a plane-wave code and apply it to several physisorbed and chemisorbed molecule-metal interface systems. Our results are in quantitative agreement with experiments, the both the level alignment and work function changes. Our approach constitutes a new practical scheme for accurate and efficient calculations of the electronic structure of molecule-metal interfaces.

Highlights

Energy level alignment can be determined by direct photoemission spectroscopy for occupied molecular orbitals and by inverse photoemission spectroscopy for unoccupied molecular orbitals.1,4–6 Conductance measurements14–16 of molecular junctions probe charge transport properties and, include indirect information about the level alignment
In principle, distinct binding geometries of molecules in junctions can lead to different level alignment17 and, charge transport properties
We developed an approach to calculate the energy level alignment at molecule-metal interfaces with good accuracy, based on an optimally tuned range-separated hybrid (OT-RSH) functional

Summary

Introduction

Energy level alignment can be determined by direct photoemission spectroscopy for occupied molecular orbitals and by inverse photoemission spectroscopy for unoccupied molecular orbitals. Conductance measurements of molecular junctions probe charge transport properties and, include indirect information about the level alignment. Energy level alignment can be determined by direct photoemission spectroscopy for occupied molecular orbitals and by inverse photoemission spectroscopy for unoccupied molecular orbitals.. Conductance measurements of molecular junctions probe charge transport properties and, include indirect information about the level alignment. In principle, distinct binding geometries of molecules in junctions can lead to different level alignment and, charge transport properties.. As charge transport measurements are usually ensemble averages of multiple geometries, care must be taken in relating the conductance to level alignment in such measurements.. First-principles electronic structure calculations that can model individual, well-defined geometries provide additional information complementary to experiments. From a formal theory viewpoint, molecular levels at interfaces are

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