Hybrid RPA:DFT Approach for Adsorption on Transition Metal Surfaces: Methane and Ethane on Platinum (111)

The hybrid QM:QM approach is extended to adsorption on transition metal surfaces. The random phase approximation (RPA) as the high-level method is applied to cluster models and, using the subtractive scheme, embedded in periodic models which are treated with density functional theory (DFT) that is the low-level method. The PBE functional, both without dispersion and augmented with the many-body dispersion (MBD), is employed. Adsorption of methane and ethane on the Pt(111) surface is studied. For methane in a 2 × 2 surface cell, the hybrid RPA:PBE and RPA:PBE+MBD results, −14.3 and −16.0 kJ mol–1, respectively, are in close agreement with the periodic RPA value of −13.8 kJ mol–1 at significantly reduced computational cost (factor of ∼50). For methane and ethane, the RPA:PBE results (−14.3 and −17.8 kJ mol–1, respectively) indicate underbinding relative to energies derived from experimental desorption barriers for relevant loadings (−15.6 ± 1.6 and −27.2 ± 2.9 kJ mol–1, respectively), whereas the hybrid RPA:PBE+MBD results (−16.0 and −24.9 kJ mol–1, respectively) agree with the experiment well within experimental uncertainty limits (deviation of −0.4 ± 1.5 and +2.3 ± 2.9 kJ mol–1, respectively). Finding a cluster that adequately and robustly represents the adsorbate at the bulk surface is important for the success of the RPA-based QM:QM scheme for metals.Norddeutscher Verbund f?r Hoch- und H?chstleistungsrechnen 10.13039/100030685Norddeutscher Verbund f?r Hoch- und H?chstleistungsrechnen 10.13039/100030685Deutsche Forschungsgemeinschaft 10.13039/501100001659Fonds der Chemischen Industrie 10.13039/100018992Peer Reviewe

Accurate Hartree-Fock energy of extended systems using large Gaussian basis sets

Calculating highly accurate thermochemical properties of condensed matter via wave function-based approaches (such as e.g. Hartree-Fock or hybrid functionals) has recently attracted much interest. We here present two strategies providing accurate Hartree-Fock energies for solid LiH in a large Gaussian basis set and applying periodic boundary conditions. The total energies were obtained using two different approaches, namely a supercell evaluation of Hartree-Fock exchange using a truncated Coulomb operator and an extrapolation toward the full-range Hartree-Fock limit of a Pad\'e fit to a series of short-range screened Hartree-Fock calculations. These two techniques agreed to significant precision. We also present the Hartree-Fock cohesive energy of LiH (converged to within sub-meV) at the experimental equilibrium volume as well as the Hartree-Fock equilibrium lattice constant and bulk modulus.Comment: 7.5 pages, 2 figures, submitted to Phys. Rev. B; v2: typos removed, References adde

Assessing the Performance of Recent Density Functionals for Bulk Solids

We assess the performance of recent density functionals for the exchange-correlation energy of a nonmolecular solid, by applying accurate calculations with the GAUSSIAN, BAND, and VASP codes to a test set of 24 solid metals and non-metals. The functionals tested are the modified Perdew-Burke-Ernzerhof generalized gradient approximation (PBEsol GGA), the second-order GGA (SOGGA), and the Armiento-Mattsson 2005 (AM05) GGA. For completeness, we also test more-standard functionals: the local density approximation, the original PBE GGA, and the Tao-Perdew-Staroverov-Scuseria (TPSS) meta-GGA. We find that the recent density functionals for solids reach a high accuracy for bulk properties (lattice constant and bulk modulus). For the cohesive energy, PBE is better than PBEsol overall, as expected, but PBEsol is actually better for the alkali metals and alkali halides. For fair comparison of calculated and experimental results, we consider the zero-point phonon and finite-temperature effects ignored by many workers. We show how Gaussian basis sets and inaccurate experimental reference data may affect the rating of the quality of the functionals. The results show that PBEsol and AM05 perform somewhat differently from each other for alkali metal, alkaline earth metal and alkali halide crystals (where the maximum value of the reduced density gradient is about 2), but perform very similarly for most of the other solids (where it is often about 1). Our explanation for this is consistent with the importance of exchange-correlation nonlocality in regions of core-valence overlap.Comment: 32 pages, single pdf fil

Assessment of correlation energies based on the random-phase approximation

The random-phase approximation to the ground state correlation energy (RPA) in combination with exact exchange (EX) has brought Kohn-Sham (KS) density functional theory one step closer towards a universal, "general purpose first principles method". In an effort to systematically assess the influence of several correlation energy contributions beyond RPA, this work presents dissociation energies of small molecules and solids, activation energies for hydrogen transfer and non-hydrogen transfer reactions, as well as reaction energies for a number of common test sets. We benchmark EX+RPA and several flavors of energy functionals going beyond it: second-order screened exchange (SOSEX), single excitation (SE) corrections, renormalized single excitation (rSE) corrections, as well as their combinations. Both the single excitation correction as well as the SOSEX contribution to the correlation energy significantly improve upon the notorious tendency of EX+RPA to underbind. Surprisingly, activation energies obtained using EX+RPA based on a KS reference alone are remarkably accurate. RPA+SOSEX+rSE provides an equal level of accuracy for reaction as well as activation energies and overall gives the most balanced performance, which makes it applicable to a wide range of systems and chemical reactions.Comment: 14 pages, 5 figures, full articl

Progress in Understanding Structure and Reactivity of Transition Metal Oxide Surfaces

Die vorliegende Habilitationsschrift bespricht aktuelle Ergebnisse zur Struktur und Reaktivität von Übergangsmetalloxidoberflächen. Es werden eingangs Grundlagen zur Berechnung von Eigenschaften von Oberflächen mittels Dichtefunktionaltheorie vorgestellt. Des Weiteren werden anhand von drei untersuchten Oxiden, nämlich dem Vanadium(III)-oxid, dem Cer(IV)-oxid, und dem Eisen(II,III)-oxid, der aktuelle Forschungsstand im Hinblick auf Oberflächenstruktur und Reaktivität von Phasengrenzen, wie z.B. der Phasengrenze zwischen Vanadium(V)-oxid und Cer(IV)-oxid und der Phasengrenze zwischen Wasser und Eisen(II,III)-oxid dargelegt.The present habilitation thesis discusses results on structure and reactivity of transition metal oxide surfaces obtained using state-of-the-art density functional theory methods. First, fundamental issues of density functional theory are presented. Furthermore, the current state in research with respect to surface structure on one hand and reactivities of interfaces between different oxides like vanadium(III) and cerium(IV) oxide or water and iron(II,III) oxide on the other hand are developed

Machine Learning in Computational Surface Science and Catalysis: Case Studies on Water and Metal–Oxide Interfaces

The goal of many computational physicists and chemists is the ability to bridge the gap between atomistic length scales of about a few multiples of an Ångström (Å), i. e., 10−10 m, and meso- or macroscopic length scales by virtue of simulations. The same applies to timescales. Machine learning techniques appear to bring this goal into reach. This work applies the recently published on-the-fly machine-learned force field techniques using a variant of the Gaussian approximation potentials combined with Bayesian regression and molecular dynamics as efficiently implemented in the Vienna ab initio simulation package, VASP. The generation of these force fields follows active-learning schemes. We apply these force fields to simple oxides such as MgO and more complex reducible oxides such as iron oxide, examine their generalizability, and further increase complexity by studying water adsorption on these metal oxide surfaces. We successfully examined surface properties of pristine and reconstructed MgO and Fe3O4 surfaces. However, the accurate description of water–oxide interfaces by machine-learned force fields, especially for iron oxides, remains a field offering plenty of research opportunities.Peer Reviewe

Defect energetics in ZnO: A hybrid Hartree-Fock density functional study

First-principles calculations based on hybrid Hartree-Fock density functionals provide a clear picture of the defect energetics and electronic structure in ZnO. Among the donorlike defects, the oxygen vacancy and hydrogen impurity, which are deep and shallow donors, respectively, are likely to form with a substantial concentration in n-type ZnO. The zinc interstitial and zinc antisite, which are both shallow donors, are energetically much less favorable. A strong preference for the oxygen vacancy and hydrogen impurity over the acceptorlike zinc vacancy is found under oxygen-poor conditions, suggesting that the oxygen vacancy contributes to nonstoichiometry and that hydrogen acts as a donor, both of which are without significant compensation by the zinc vacancy. The present results show consistency with the relevant experimental observations

Editorial: Interfacial Structures and Their Properties

Peer Reviewe

Adsorption of Water on the Fe₃O₄(111) Surface: Structures, Stabilities, and Vibrational Properties Studied by Density Functional Theory

The majority of the theoretical work that attempted to provide atomic level details on the adsorption of water at the Fe₃O₄(111) surface is based on conventional density functionals, which suffer from shortcomings such as, for example, self-interaction errors. In an effort to overcome these uncertainties in theoretical results, we use density functional theory (DFT) employing the Perdew, Burke, and Ernzerhof generalized-gradient corrected exchange-correlation functional augmented by a Hubbard-type <i>U</i> parameter. We test for robustness of these results by application of the Heyd, Scuseria, Ernzerhof hybrid functional. For the two relevant metal terminations (Fe_oct2 and Fe_tet1) having ambient conditions in mind, we determined the minimum energy adsorption structures up to relatively high water coverage, that is, one, two, and three H₂O molecules on the <i>p</i>(1 × 1) surface unit cells, respectively. Water adsorbs dissociatively and strongly exothermic on the Fe_oct2, whereas molecular adsorption occurs on the Fe_tet1 termination. Using D₂O, two IR signals at 2720 and 2695 cm^–1 (typical of OD stretching modes) can be observed for a wide range of temperatures and at moderate water vapor pressures. Our calculations reveal that these IR bands originate from a very stable water dimer-like species. However, at lower temperatures the creation of larger aggregations, such as trimers, appears to be thermodynamically favorable