Topological Stone–Wales Defects Enhance Bonding and Electronic Coupling at the Graphene/Metal Interface

B. P. Klein, A. Ihle, S. R. Kachel, L. Ruppenthal, S. J. Hall, L. Sattler, S. M. Weber, J. Herritsch, A. Jaegermann, D. Ebeling, R. J. Maurer, G. Hilt, R. Tonner-Zech, A. Schirmeisen, J. M. Gottfried, ACS Nano 16, 11979-11987 (2022)

"Defects in Graphene subtly affect the structural and electronic properties. We perform a detailed joint experiment/theory investigation of molecular precursors of pristine graphene and Stone-Wales defects in graphene to assess the structural and spectroscopic changes imposed by defects."

Long-range dispersion-inclusive machine learning potentials for structure search and optimization of hybrid organic–inorganic interfaces

J. Westermayr, S. Chaudhuri, A. Jeindl, O. T. Hofmann, R. J. Maurer, Digital Discovery DOI:10.1039/D2DD00016D (2022)

"We present an ML approach that enables fast, yet accurate, structure optimizations by combining two different types of deep neural networks trained on high-level electronic structure data. The first model is a short-ranged interatomic ML potential trained on local energies and forces, while the second is an ML model of effective atomic volumes derived from atoms-in-molecules partitioning. The latter can be used to connect short-range potentials to well-established density-dependent long-range dispersion correction methods. For two systems, specifically gold nanoclusters on diamond (110) surfaces and organic π-conjugated molecules on silver (111) surfaces, we show the ability of the models to deliver highly efficient structure optimizations and semi-quantitative energy predictions of adsorption structures."

Dissipative tunneling rates through the incorporation of first-principles electronic friction in instanton rate theory. II. Benchmarks and applications

Y. Litman, E. S. Pos, C. L. Box, R. Martinazzo, R. J. Maurer, M. Rossi J. Chem. Phys. 156, 194107 (2022)

"Hydrogen chemistry at surfaces can involve nonadiabatic effects (NAEs) and quantum nuclear effects (NQEs). The theoretical modeling of such reactions presents a formidable challenge for theory. In this work, we derive a theoretical framework that captures both NQEs and NAEs and, due to its high efficiency, can be applied to first-principles calculations of reaction rates in high-dimensional realistic systems. More specifically, we develop a method that we coin ring polymer instanton with explicit friction, starting from the ring polymer instanton formalism applied to a system–bath model. In this second part, we present benchmark calculations and applications."

Dissipative tunneling rates through the incorporation of first-principles electronic friction in instanton rate theory. I. Theory

Y. Litman, E. S. Pos, C. L. Box, R. Martinazzo, R. J. Maurer, M. Rossi J. Chem. Phys. 156, 194106 (2022)

"Hydrogen chemistry at surfaces can involve nonadiabatic effects (NAEs) and quantum nuclear effects (NQEs). The theoretical modeling of such reactions presents a formidable challenge for theory. In this work, we derive a theoretical framework that captures both NQEs and NAEs and, due to its high efficiency, can be applied to first-principles calculations of reaction rates in high-dimensional realistic systems. More specifically, we develop a method that we coin ring polymer instanton with explicit friction, starting from the ring polymer instanton formalism applied to a system–bath model. In this first part, we describe the theory and derivation of this approach."

NQCDynamics.jl: A Julia Package for Nonadiabatic Quantum Classical Molecular Dynamics in the Condensed Phase

J. Gardner, O. A. Douglas-Gallardo, W. G. Sark, J. Westermayr, S. M. Janke, S. Habershon, R. J. Maurer, J. Chem. Phys. 156, 174801 (2022)

"Using the Julia programming language, we have developed the NQCDynamics.jl package which provides a framework for established and emerging methods for performing semiclassical and mixed quantum-classical dynamics in condensed phase. The code provides several interfaces to existing atomistic simulation frameworks, electronic structure codes, and machine learning representations."

Direct Experimental Evidence for Substrate Adatom Incorporation into a Molecular Overlayer

P. J. Mouslez, L. A. Rochford, P. T. P. Ryan, P. Blowey, J. Lawrence, D. A. Duncan, H. Hussain, B. Sohail, T.-L. Lee, G. R. Bell, G. Costantini, R. J. Maurer, C. Nicklin, D. P. Woodruff, J. Phys. Chem. C 126, 7346 - 7355 (2022)

"We present the results of a detailed structural study of the Au(111)-F₄TCNQ system, combining surface characterization by STM, low-energy electron diffraction, and soft X-ray photoelectron spectroscopy with quantitative experimental structural information from normal incidence X-ray standing wave (NIXSW) and SXRD, together with dispersion-corrected density functional theory (DFT) calculations. SXRD measurements provide unequivocal evidence for the presence and location of Au adatoms, while the DFT calculations show this reconstruction to be strongly energetically favored"

Design Principles for Metastable Standing Molecules

H. H. Arefi, D.Corken, F. S.Tautz, R. J. Maurer, C. Wagner, J. Phys. Chem. C 126, 6880-6891 (2022)

"Here, we use density functional theory to study 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) standing on the Ag(111) surface as well as on the tip of a scanning probe microscope. We cast our results into a simple set of design principles for such metastable structures, the validity of which we subsequently demonstrate in two computational case studies. Our work proves the capabilities of computational nanostructure design in the field of metastable molecular structures and offers the intuition needed to fabricate new devices without tedious trial and error."

Thermodynamic Driving Forces for Substrate Atom Extraction by Adsorption of Strong Electron Acceptor Molecules

P. Ryan, P. J. Blowey, B. S. Sohail, L. A. Rochford, D. A. Duncan, T.-L. Lee, P. Starrs, G. Costantini, R. J. Maurer, J. Phys. Chem. C 126, 6082-6090 (2022)

"A quantitative structural investigation is reported, aimed at resolving the issue of whether substrate adatoms are incorporated into the monolayers formed by strong molecular electron acceptors deposited onto metallic electrodes. A combination of X-ray standing waves, STM, and DFT show that there is an energetic driving force for adatom incorporation into adsorbate structures of the strong acceptor F₄TCNQ on Ag(100) but not for the weaker acceptor TCNQ."

Effect of electron donating/withdrawing groups on molecular photoswitching of functionalized hemithioindigo derivatives: a computational multireference study

M. Lea, V. Stavros, R. J. Maurer, ChemPhotoChem, DOI: 10.1002/cptc.202100290 (2022)

"The mechanism of photoswitching for hemithioindigo cannot be described by pure dihedral rotation around the central carbon-carbon bond. A complementary motion, often pyramidalization, is required to facilitate radiationless internal conversion. This computational study, explores how the inclusion of electron-withdrawing and electron-donating substituents alters the excited state potential energy surfaces and the mechanism of photoisomerization. The predicted changes in energy landscapes reflect the acceleration or slowing of the photoisomerization process for different derivatives that is also observed in experiment."

Roadmap on Machine Learning in Electronic Structure

Kulik et al., IOP Electronic Structure DOI: 10.1088/2516-1075/ac572f (2022)

"A perspective roadmap that covers the present role and future perspective of machine learning in materials property prediction, the construction of accurate force fields, the solution of the many-body problem, and big data challenges."

Coexistence of carbonyl and ether groups on oxygen-terminated (110)-oriented diamond surfaces

Shayanthan Chaudhuri, Samuel J. Hall, Benedikt P. Klein, Marc Walker, Andrew J. Logsdail, Julie V. Macpherson, Reinhard J. Maurer, Communications Materials 3, 6 (2022)

"Here, we determine the oxygenation state of the (110) surface using a combination of density functional theory calculations and X-ray photoelectron spectroscopy experiments. We report the fabrication of the highest-quality (100)-oriented diamond crystal surface to date. We further propose a mechanism for the formation of the hybrid carbonyl-ether phase and rationalize its high stability. "

Core Electron Binding Energies in Solids from Periodic All-Electron Delta-Self-Consistent-Field Calculations

J. Matthias Kahk, Georg S. Michelitsch, Reinhard J. Maurer, Karsten Reuter, Johannes Lischner, J. Phys. Chem. Lett. 12, 9353-9359 (2021)

"We present an approach to calculate accurate core electron binding energies of a variety of materials based on Delta-self-consistent-field calculations that are referenced to the valence band maximum. We further show that the resulting simulations provide excellent agreement with experimental X-ray photoemission spectroscopy data."

Adiabatic versus non-adiabatic electron transfer at 2D electrode materials

Dan-Qing Liu, Minkyung Kang, David Perry, Chang-Hui Chen, Geoff West, Xue Xia, Shayantan Chaudhuri, Zachary P. L. Laker, Neil R. Wilson, Gabriel N. Meloni, Marko M. Melander, Reinhard J. Maurer, Patrick R. Unwin, Nature Communications 12, 7110 (2021)

"Using scanning electrochemical cell microscopy, and co-located structural microscopy, the classical hexaamineruthenium (III/II) couple is measured on a graphene-metal electrode. Using model Hamiltonian and constant potential density functional theory, we can rationalize the fact that monolayer graphene shows faster kinetics than bilayer graphene and we are able to identify the electron transfer as dominantly adiabatic."

Nature Portfolio Blogpost

The stabilization potential of a standing molecule

Marvin Knol, Hadi H. Arefi, Daniel Corken, James Gardner, F. Stefan Tautz, Reinhard J. Maurer, and Christian Wagner, Science Advances 7, eabj9751 (2021)

"Here, we combine scanning probe experiments with ab initio potential energy calculations to investigate the thermal stability of a prototypical standing molecule. We reveal its generic stabilization mechanism, a fine balance between covalent and van der Waals interactions including the latter's long-range screening by many-body effects, and find a remarkable agreement between measured and calculated stabilizing potentials."

Warwick University Press Release

Physically inspired deep learning of molecular excitations and photoemission spectra

Julia Westermayr, Reinhard J. Maurer, Chemical Science 12, 10755-10764 (2021)

"In this work, we present a deep neural network that predicts charged quasiparticle excitations for large and complex organic molecules with a rich elemental diversity and a size well out of reach of accurate many body perturbation theory calculations."

Perspective on integrating machine learning into computational chemistry and materials science

Julia Westermayr, Michael Gastegger, Kristof T. Schütt, Reinhard J. Maurer, J. Chem. Phys. 154, 230903 (2021)

"As ML is becoming pervasive in electronic structure theory and molecular simulation, we provide an overview of how atomistic computational modeling is being transformed by the incorporation of ML approaches. From the perspective of the practitioner in the field, we assess how common workflows to predict structure, dynamics, and spectroscopy are affected by ML."

Plasmonic enhancement of molecular hydrogen dissociation on metallic magnesium nanoclusters

Oscar Douglas-Gallardo, Connor L. Box, Reinhard J. Maurer, Nanoscale 13, 11058-11068 (2021)

"The optical and catalytic properties of magnesium nanoclusters are characterized in the context of plasmonic catalysis. Our Time-Dependent DFTB and DFT simulations show that plasmonic enhancement of hydrogen dissociation and evolution on magnesium nanoclusters is viable."

Topology Effects in Molecular Organic Electronics Materials: Pyrene and Azupyrene

Benedikt P. Klein, Lukas Ruppenthal, Samuel J. Hall, Lars E Sattler, Sebastian M. Weber, Jan Herritsch, Andrea Jaegermann, Reinhard J. Maurer, Gerhard Hilt, and Michael Gottfried, ChemPhysChem 22, 1-10 (2021)

"Using photoelectron spectroscopy, near edge X-ray absoption fine structure spectroscopy, and density functional theory, we characterize the electronic and optical properties of pyrene and azupyrene thin films. The differences between the properties of the two compounds can be understood in terms of their different bonding topology."

First-principles calculations of hybrid inorganic-organic interfaces: From state-of-the-art to best practice

Oliver T. Hofmann, Egbert Zojer, Lukas Hörmann, Andreas Jeindl, and R. J. Maurer, Phys. Chem. Chem. Phys. 23, 8132-8180 (2021)

"In this review, we discuss how to choose appropriate atomistic representations for the simulation of hybrid inorganic-organic interfaces. We provide tips and tricks on how to efficiently converge the self-consistent field cycle and to obtain accurate geometries. We particularly focus on potentially unexpected pitfalls and the errors they incur. As a summary, we provide a list of best practice rules for interface simulations that should especially serve as a useful starting point for less experienced users and newcomers to the field."

The Nuts and Bolts of Ab-Initio Core-Hole Simulations for K-shell X-Ray Photoemission and Absorption Spectra

B. Klein, S. J. Hall, R. J. Maurer, J. Phys. Condens. Matter 33, 154005 (2020)

"We present the numerical and technical details of our variants of the DeltaSCF and transition potential method (coined DeltaIP-TP) to simulate XPS and NEXAFS transitions. Using exemplary molecules in gas-phase, in bulk crystals, and at metal-organic interfaces, we systematically assess how practical simulation choices affect the stability and accuracy of simulations. We particularly focus on the choice of aperiodic or periodic description of systems and how spurious charge effects in periodic calculations affect the simulation outcomes. For the benefit of practitioners in the field, we discuss sensible default choices, limitations of the methods, and future prospects."

Determining the effect of hot electron dissipation on molecular scattering experiments at metal surfaces

C. L. Box, Y. Zhang, R. Yin, B. Jiang, R. J. Maurer, JACS Au 1, 164-173 (2020)

"Vibrational state-to-state scattering of NO on Au(111) provides a testing ground for developing various nonadiabatic theories, including electronic friction theory. This system is often cited as the prime example for the breakdown of electronic friction theory, a very efficient model accounting for dissipative forces on metal-adsorbed molecules due to the creation of electron-hole-pair excitations in the metal. Here we present a comprehensive quantitative analysis of the performance of molecular dynamics with electronic friction (MDEF) in describing vibrational state-to-state scattering of NO on Au(111) and connect directly to fundamental approximations. Our analysis provides a firm baseline for the future development of nonadiabatic dynamics methods to tackle problems in surface chemistry and photocatalysis."

A deep neural network for molecular wave functions in quasi-atomic minimal basis representation

M. Gastegger, A. McSloy, M. Luya, K. T. Schütt, R. J. Maurer, J. Chem. Phys 153, 044123 (2020)

"We present an adaptation of the recently proposed SchNet for Orbitals (SchNOrb) deep convolutional neural network model [Nature Commun. 10, 5024 (2019)] for electronic wave functions in an optimised quasi-atomic minimal basis representation. For five organic molecules ranging from 5 to 13 heavy atoms, the model accurately predicts molecular orbital energies and wavefunctions and provides access to derived properties for chemical bonding analysis. Particularly for larger molecules, the model outperforms the original atomic-orbital-based SchNOrb method in terms of accuracy and scaling. "

Alkali Doping Leads to Charge-Transfer Salt Formation in a Two-Dimensional Metal-Organic Framework

P. J. Blowey, B. Sohail, L. A. Rochford, T. Lafosse, D. A. Duncan, P. T. P. Ryan, D. A. Warr, T.-L. Lee, G. Costantini, R. J. Maurer, and D. P. Woodruff, ACS Nano 14, 7475-7483 (2020)

"We show that the insertion of alkali atoms can significantly change the structure and electronic properties of a metal-organic interface. Coadsorption of tetracyanoquinodimethane (TCNQ) and potassium on a Ag(111) surface leads to the formation of a two-dimensional charge transfer salt, with properties quite different to those of the two-dimensional Ag adatom TCNQ metal-organic framework formed in the absence of K doping. We establish a highly accurate structural model by combination of quantitative XSW, STM, and DFT calculations. Full agreement between the experimental data and the computational prediction of the structure is only achieved by inclusion of a charge-transfer-scaled dispersion correction in the DFT, which correctly accounts for the effects of strong charge transfer on the atomic polarizability of potassium. "

DFTB+, a software package for efficient approximate density functional theory based atomistic simulations

B. Hourahine, B. Aradi et al., J. Chem. Phys. 152, 124101 (2020)

"DFTB+ is a versatile community developed open source software package offering fast and efficient methods for carrying out atomistic quantum mechanical simulations. We give an overview of the recently developed capabilities of the DFTB+ code, demonstrating with a few use case examples, discuss the strengths and weaknesses of the various features, and also discuss on-going developments and possible future perspectives."

Enhanced Bonding of Pentagon–Heptagon Defects in Graphene to Metal Surfaces: Insights from the Adsorption of Azulene and Naphthalene to Pt(111)

Benedikt P. Klein, S. Elizabeth Harman, Lukas Ruppenthal, Griffin M. Ruehl, Samuel J. Hall, Spencer J. Carey, Jan Herritsch, Martin Schmid, Reinhard J. Maurer, Ralf Tonner, Charles T. Campbell, and J. Michael Gottfried, Chem. Mater. 32, 1041-1053 (2020)

"We show here that the interface properties may be controlled by topological defects, such as the pentagon–heptagon (5–7) pairs, because of their strongly enhanced bonding to the metal. To measure the bond energy and other key properties not accessible for the embedded defects, we use azulene as a molecular model for the 5–7 defect. Comparison to its isomer naphthalene, which represents the regular graphene structure, reveals that azulene interacts more strongly with a Pt(111) surface. Using a combination of single-crystal adsorption calorimetry, x-ray photoelectron and photoabsorption spectroscopies (XPS/NEXAFS), and Density Functional Theory, we fully characterize the adsorption strength, the surface structure and surface chemistry of 5-7 defect systems on Pt(111). Our model study shows that the topology of the π-electron system strongly affects its bonding to a transition metal and thus can be utilized to tailor interface properties."

A symmetry adapted high dimensional neural network representation of electronic friction tensor of adsorbates on metals

Yaolong Zhang, Reinhard J. Maurer, Bin Jiang, J. Chem. Phys., just accepted (2019)

"In this work, we develop a new symmetry-adapted neural network representation of electronic friction, based on our recently proposed embedded atom neural network (EANN) framework. Unlike previous methods, our new approach can readily include both molecular and surface degrees of freedom, regardless of the type of surface. Tests on the H2+Ag(111) system show that this approach yields an accurate, efficient, and continuous representation of electronic friction, making it possible to perform large scale TDPT-based MDEF simulations to study both adiabatic and nonadiabatic energy dissipation in a unified framework."

Unifying machine learning and quantum chemistry with a deep neural network for molecular wavefunctions

Kristof T. Schütt, Michael Gastgger, Alexandre Tkatchenko, Klaus-Robert Müller, Reinhard J. Maurer, Nature Commun. 10, 5024 (2019)

"Here we present a deep machine learning framework for the prediction of the quantum mechanical wavefunction in a local basis of atomic orbitals from which all other ground-state properties can be derived. This approach retains full access to the electronic structure via the wavefunction at force-field-like efficiency and captures quantum mechanics in an analytically differentiable representation. On several examples, we demonstrate that this opens promising avenues to perform inverse design of molecular structures for targeting electronic property optimisation and a clear path towards increased synergy of machine learning and quantum chemistry."

Molecule–Metal Bond of Alternant versus Nonalternant Aromatic Systems on Coinage Metal Surfaces: Naphthalene versus Azulene on Ag(111) and Cu(111)

Benedikt P. Klein, Juliana M. Morbec, Markus Franke, Katharina K. Greulich, Malte Sachs, Shayan Parhizkar, Francois C. Boquet, Martin Schmidt, Samuel J. Hall, Reinhard J. Maurer, Bernd Meyer, Ralf Tonner, Christian Kumpf, Peter Kratzer, and J. Michael Gottfried, J. Phys. Chem. C just accepted, DOI: 10.1021/acs.jpcc.9b08824 (2019)

"The coverage-dependent interaction of Azulene and Naphthalene with Ag(111) and Cu(111) surfaces was studied with the normal-incidence X-ray standing wave (NIXSW) technique, near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, UV and X-ray photoelectron spectroscopies (UPS and XPS), and density functional theory (DFT). We analyse the interaction strength and charge-transfer at the molecule-metal interface by comparing simulated and measured NEXAFS spectra."

Molecular Topology and the Surface Chemical Bond: Alternant Versus Nonalternant Aromatic Systems as Functional Structural Elements

Benedikt P. Klein, N. J. van der Heijden, S. R. Kachel, M. Franke, C. K. Krug, K. K. Greulich, L. Ruppenthal, P. Müller, P. Rosenow, S. Parhizkar, F. C. Bocquet, M. Schmid, W. Hieringer, R. J. Maurer, R. Tonner, C. Kumpf, I. Swart, J. M. Gottfried, Phys. Rev. X 9, 011030 (2019).

"Using a wide range of experimental techniques and Density Functional Theory calculations, we characterize the changes in molecule-metal binding between an alternant and a non-alternant aromatic molecule.Our results indicate that the electronic properties of metal-organic interfaces, as they occur in organic (opto)electronic devices, can be tuned through modifications of the molecular topology of the molecular organic semiconductor."

Advances in Density-Functional Calculations for Materials Modeling

Reinhard J. Maurer, Christoph Freysoldt, Anthony M. Reilly, Jan Gerit Brandenburg, Oliver T. Hofmann, Torbjörn Björkman, Sébastien Lebègue, and Alexandre Tkatchenko. Annual Review of Materials Research, 49:1, 1-30, ( 2019)

During the past two decades, density-functional (DF) theory has evolved from niche applications for simple solid-state materials to become a workhorse method for studying a wide range of phenomena in a variety of system classes throughout physics, chemistry, biology, and materials science. Here, we review the recent advances in DF calculations for materials modeling, giving a classification of modern DF-based methods when viewed from the materials modeling perspective. While progress has been very substantial, many challenges remain on the way to achieving consensus on a set of universally applicable DF-based methods for materials modeling. Hence, we focus on recent successes and remaining challenges in DF calculations for modeling hard solids, molecular and biological matter, low-dimensional materials, and hybrid organic-inorganic materials.

https://www.annualreviews.org/doi/abs/10.1146/annurev-matsci-070218-010143