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."

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."

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

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."

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."

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."

Performance of van der Waals DFT approaches for helium diffraction on metal surfaces

Marcos del Cueto, Reinhard Maurer, Amjad Al Taleb, Daniel Farias, Fernando Martin and Cristina Diaz, J. Phys.: Condens. Matter 31, 135901 (2019).

"The ability of the different approaches proposed to date to include the effects of van der Waals (vdW) dispersion forces in density functional theory (DFT) is currently under debate. Here, we used the diffraction of He on a Ru(0001) surface as a challenging benchmark system to analyze the suitability of several representative approaches, from the ones correcting the exchange-correlation generalized gradient approximation (GGA) functional, to the ones correcting the DFT energies through pairwise-based methods. To perform our analysis, we have built seven continuous potential energy surfaces (PESs) and carried out quantum dynamics simulations using a multi-configuration time-dependent Hartree (MCTDH) method. Our analysis reveals that standard DFT within the PBE-GGA framework, although it overestimates diffraction probabilities, yields the best results in comparison with available experimental measurements."

Adhesion, forces and the stability of interfaces

Robin Guttmann, Johannes Hoja, Christoph Lechner, Reinhard J. Maurer, and Alexander F. Sax, Beilstein J. Org. Chem., 15, 106–129. (2019)

"Weak molecular interactions (WMI) are responsible for processes such as physisorption; they are essential for the structure and stability of interfaces, and for bulk properties of liquids and molecular crystals. For a long time, dispersion was largely ignored in chemistry, attractive intermolecular interactions were nearly exclusively attributed to electrostatic interactions. We discuss the importance of dispersion interactions for the stabilization in systems that are traditionally explained in terms of the “special interactions” mentioned above."

https://www.beilstein-journals.org/s/eDT9bbVnb5

Structure and Stability of Molecular Crystals with Many Body Dispersion Inclusive Density Functional Tight Binding

Majid Mortazavi, Jan Gerit Brandenburg, Reinhard J. Maurer, Alexandre Tkatchenko, J. Phys. Chem. Lett. 9, 399-405 (2018)

"We show the ability of many-body-dispersion-inclusive tight-binding methodology to accurately predict the structure of polymorphic organic molecular crystals."

Interpretation of X-ray Absorption Spectroscopy in the Presence of Surface Hybridisation

Katharina Diller, Reinhard J. Maurer, Moritz Müller, Karsten Reuter, J. Chem. Phys. 146, 214701 (2017)

Accurate ab-initio core-level spectroscopy simulations of surface-adsorbed molecules reveal the details of surface hybridization.

Switching of an Azobenzene-Tripod Molecule on Ag(111)

Katharina Scheil, Thiruvancheril G. Gopakumar, Julia Bahrenburg, Friedrich Temps, Reinhard J. Maurer, Karsten Reuter, Richard Berndt, J. Phys. Chem. Lett. 7, 2080-2084 (2016)

We observe and interpret the mechanism of multistate switching of an Azobenzene Tripod on Ag(111) using STM, STS and Density Functional Theory.

Adsorption structures and energetics of molecules on metal surfaces: Bridging experiment and theory

Reinhard J. Maurer, Victor G. Ruiz, Javier Camarillo-Cisneros, Wei Liu, Nicola Ferri, Karsten Reuter, Alexandre Tkatchenko, Prog. Surf. Sci. 91, 72-100 (2016)

By reviewing experiment and calculation data for structures and energies, we compose a benchmark database for molecules on metal surfaces.

Charge-Population Based Dispersion Interactions for Molecules and Materials

Martin Stöhr, Georg S. Michelitsch, John C. Tully, Karsten Reuter, Reinhard J. Maurer, J. Chem. Phys., 144, 151101 (2016)

A simple correlation between atomic polarizability and hybridization enables us to couple semi-empirical electronic structure methods with electron density-derived dispersion correction methods.

Thermal and electronic fluctuations of flexible adsorbed molecules: Azobenzene on Ag(111)

Reinhard J. Maurer, Wei Liu, Igor Poltavsky, Thomas Stecher, Harald Oberhofer, Karsten Reuter, Alexandre Tkatchenko, Phys. Rev. Lett., 116, 146101 (2016)

Ab Initio molecular dynamics simulation of the free energy of desorption reveals collective electronic and thermal fluctuations that define the finite-temperature energetics of complex adsorbates.

Interfacial charge rearrangement and intermolecular interactions: Density-functional theory study of free-base porphine adsorbed on Ag(111) and Cu(111)

M. Müller, K. Diller, R. J. Maurer, K. Reuter, J. Chem. Phys., 144, 024701 (2016)

We study the interactions and the self-assembly behaviour of Porphine on Ag(111) and Cu(111). We find significant substrate-mediated, and negligible direct lateral interactions.

Adsorption of Glucose, Cellobiose, and Cellotetraose onto Cellulose Model Surfaces

J. Hoja, R. J. Maurer, A. F. Sax, J. Phys. Chem. B 118, 9017-9027(2014)

We analyse the interplay of dispersion and hydrogen bonding interactions of small carbohydrates on cellulose surfaces