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We investigate the gas-phase structure of the neutral pentaalanine peptide. The IR spectrum in the 340-1820 cm-1 frequency range is obtained by employing supersonic jet cooling, infrared multiphoton dissociation, and vacuum-ultraviolet action spectroscopy. Comparison with quantum chemical spectral calculations suggests that the molecule assumes multiple stable conformations, mainly of two structure types. In the most stable conformation theoretically found, the N-terminus forms a C5 ring and the backbone resembles that of an 310-helix with two beta-turns. Additionally, the conformational preferences of pentaalanine have been evaluated using Born-Oppenheimer molecular dynamics, showing that a nonzero simulation time step causes a systematic frequency shift. Funding Agencies|Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO); Swedish Research Council [2019-04439]

Methylation of aromatic compounds is a key reaction step in various industrial processes such as the aromatic cycle of methanol-to-hydrocarbons chemistry. The study of isolated methylation reactions and of the influence of catalyst acidity on their kinetics is a challenging task. Herein, we have studied unidirectional metal-substituted H-MeAlPO-5 materials to evaluate the effect of acid strength on the kinetics of benzene methylation with DME. First-principle simulations showed a direct correlation between the methylation barrier and acid site strength, which depends on the metal substituent. Three H-MeAlPO5 catalysts with high (Me = Mg), moderate (Me = Si) and low acidity (Me = Zr) were experimentally tested, confirming a linear relationship between the methylation activation energy and acid strength. The effects of temperature and reactant partial pressure were evaluated, showing significant differences in the byproduct distribution between H-MgAlPO-5 and H-SAPO-5. Comparison with propene methylation suggested that the Mg substituted catalyst is also the most active for the selective methylation of alkenes. (c) 2021 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Steps at metal surfaces may influence energetics and kinetics of catalytic reactions in unexpected ways. Here, we report a significant reduction of the CO saturation coverage in Pd vicinal surfaces, which in turn is relevant for the light-off of the CO oxidation reaction. The study is based on a systematic investigation of CO adsorption on vicinal Pd(111) surfaces making use of a curved Pd crystal. A combined X-ray Photoelectron Spectroscopy and DFT analysis allows us to demonstrate that an entire row of atomic sites under Pd steps remains free of CO upon saturation at 300 K, leading to a step-density-dependent reduction of CO coverage that correlates with the observed decrease of the light-off temperature during CO oxidation in vicinal Pd surfaces., We acknowledge financial support from the Spanish Ministry of Science and Innovation (Grants MAT-2017-88374-P, PID2019-107338RB-C63, PID2020-116093RB-C44), the Basque Government (Grants IT-1255-19), the Knut and Alice Wallenberg foundation (DNR KAW 2015.0058 ”Atomistic Design of new Catalysts”), and the Swedish Research Council (DNR 349-2011-6491 “Catalysis on the Atomic Scale”). Financial support is acknowledged from the Swedish Research Council (2016-5234). The DFT calculations were performed at C3SE (Göteborg) via a SNIC grant. We acknowledge MAX IV Laboratory support, in particular Alexei Preobrajenski, for their help in synchrotron experiments, which were carried out at the FlexPES beamline under Proposal 20190717. Research conducted at MAX IV, a Swedish national user facility, is supported by the Swedish Research council under contract 2018-07152, the Swedish Governmental Agency for Innovation Systems under contract 2018-04969, and Formas under contract 2019-02496. Moreover, the research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020.

We propose to analyze molecular dynamics (MD) output via a supervised machine learning (ML) algorithm, the decision tree. The approach aims to identify the predominant geometric features which correlate with trajectories that transition between two arbitrarily defined states. The data-driven algorithm aims to identify these features without the bias of human “chemical intuition”. We demonstrate the method by analyzing the proton exchange reactions in formic acid solvated in small water clusters. The simulations were performed with ab initio MD combined with a method to efficiently sample the rare event, path sampling. Our ML analysis identified relevant geometric variables involved in the proton transfer reaction and how they may change as the number of solvating water molecules changes.

Two-dimensional nanoporous covalent organic frame-works (2D COFs) have gathered significant interest due to their wide range of applications. Due to the lack of strong covalent interlayer interactions, their layers can be stacked in countless ways, each resulting in unique nanoscale characteristics impacting the structural, chemical, and electronic properties. To characterize and understand the layer stacking in 2D COFs and its effect on the structural and electronic properties, we carried out a detailed density functional theory investigation on four materials, CTF-1, COF-1, COF-5, and Pc-PBBA. This entailed an in-depth evaluation of the potential energy as a function of the interlayer distance and offset, the powder X-ray diffraction (PXRD) pattern, and the electronic properties. From the potential energy surfaces, the typical slipped AA-stacking configuration was confirmed as optimal for each of the 2D COFs, with a slight offset from a perfect alignment of the layers. The statically calculated PXRD patterns based on these optimized stacking configurations showed discrepancies when compared to experimental data. Instead, when properly accounting for dynamic fluctuations by calculating the average diffraction pattern over the course of a molecular dynamics simulation, a better agreement with the experiment is obtained. Different stacking configurations also profoundly affected the electronic band structure of COFs as the interlayer pi-pi interactions are significantly impacted by the layer offset. Evidently, with decreasing layer offsets, the pi-pi interactions increase due to the layer alignment, leading to a decrease in the band gap and an increase in interlayer charge mobility. Our study highlights the need for accurate modeling of the stacking configuration in 2D COFs as a small-scale deviation in the adjacent layer position can significantly affect the structural and electronic properties.

The renewable-electricity-powered CO2 electroreduction reaction provides a promising means to store intermittent renewable energy in the form of valuable chemicals and dispatchable fuels. Renewable methane produced using CO2 electroreduction attracts interest due to the established global distribution network; however, present-day efficiencies and activities remain below those required for practical application. Here we exploit the fact that the suppression of *CO dimerization and hydrogen evolution promotes methane selectivity: we reason that the introduction of Au in Cu favors *CO protonation vs. C−C coupling under low *CO coverage and weakens the *H adsorption energy of the surface, leading to a reduction in hydrogen evolution. We construct experimentally a suite of Au-Cu catalysts and control *CO availability by regulating CO2 concentration and reaction rate. This strategy leads to a 1.6× improvement in the methane:H2 selectivity ratio compared to the best prior reports operating above 100 mA cm−2. We as a result achieve a CO2-to-methane Faradaic efficiency (FE) of (56 ± 2)% at a production rate of (112 ± 4) mA cm−2., The electroreduction of CO2 offers a promising approach to produce carbon-neutral methane using renewable electricity. This study shows that the introduction of Au in Cu enables selective methane production from CO2 by regulating *CO availability.

Accurate and efficient simulation of liquids, such as water and salt solutions, using high-level wave function theories is still a formidable task for computational chemists owing to the high computational costs. In this study, we develop a deep machine learning potential based on fragment-based second-order Moller-Plesset perturbation theory (DP-MP2) for water through neural networks. We show that the DP-MP2 potential predicts the structural, dynamical, and thermodynamic properties of liquid water in better agreement with the experimental data than previous studies based on density functional theory (DFT). The nuclear quantum effects (NQEs) on the properties of liquid water are also examined, which are noticeable in affecting the structural and dynamical properties of liquid water under ambient conditions. This work provides a general framework for quantitative predictions of the properties of condensed-phase systems with the accuracy of high-level wave function theory while achieving significant computational savings compared to ab initio simulations.

Hard carbons have shown considerable promise as anodes for emerging sodium-ion battery technologies. Current understanding of sodium-storage behaviour in hard carbons attributes capacity to filling of graphitic interlayers and pores, and adsorption at defects, although there is still considerable debate regarding the voltages at which these mechanisms occur. Here, ex situ23Na solid-state NMR and total scattering studies on a systematically tuned series of hard carbons revealed the formation of increasingly metallic sodium clusters in direct correlation to the growing pore size, occurring only in samples which exhibited a low voltage plateau. Combining experimental results with DFT calculations, we propose a revised mechanistic model in which sodium ions store first simultaneously and continuously at defects, within interlayers and on pore surfaces. Once these higher energy binding sites are filled, pore filling occurs during the plateau region, where the densely confined sodium takes on a greater degree of metallicity.

A new algorithm for efficient and fully time-reversible integration of first-principles molecular dynamics based on orbital-free density functional theory (OFDFT) is presented. The algorithm adapts to this nontrivial case, the recently introduced Mass-Zero (MaZe) constrained dynamics. The formalism ensures that full adiabatic separation is enforced between nuclear and electronic degrees of freedom and, consequently, that the exact Born–Oppenheimer probability for the nuclei is sampled. Numerical integration of the MaZe dynamics combines standard molecular dynamics algorithms, e.g., Verlet or velocity Verlet, with the SHAKE method to impose the minimum conditions on the electronic degrees of freedom as a set of constraints. The developments presented in this work, which include a bespoke adaptation of the standard SHAKE algorithm, ensure that the quasilinear scaling of OFDFT is preserved by the new method for a broad range of kinetic and exchange–correlation functionals, including nonlocal ones. The efficiency and accuracy of the approach are demonstrated via calculations of static and dynamic properties of liquid sodium in the constant energy and constant temperature ensembles.

The water splitting is an appealing approach to fulfil the demand of energy without any global concerns. The oxygen evolution reaction is one of way to achieve unlimited energy from water but the low stability, high energy required to drive the reaction (overpotential), complicated and unscalable synthesis method of expensive catalysis restricts its real time implementation into modern society. Herein this report, we suggested Ru-tailored hydrous cobalt phosphate and its concentration effect as a dopant to improve the catalytic properties. Electrocatalytic properties were studied via linear sweep voltammetry, chrono-potentiometric studies at a 10 mA/cm2 for 20 h, electrochemical active surface area, turnover fre-quency, and Tafel slope. Cobalt phosphate showed the connected-nanorods morphology, which is further tunned by increasing Ru-doping concentration, achieving various features from agglomerated nanorods sensitized with uniform nanoparticles on the micro -flower shapes consisting of interconnected nanorods sensitized with nanoparticles. The good electrocatalytic OER performance of 5% Ru-doped hydrous cobalt phosphate was achieved, exhibiting low overpotential up to 310 mV (vs. RHE) at 10 mA/cm2 besides a small Tafel slope of 62 mV/dec in 1 M KOH. As well, stable O2 evolution for a period of 20 h was shown. DFT calculation reveals that the Ru can increase electrical conductivity and promote OER activity, observed from Bader charge analysis, electron density difference, and OER Gibbs free energy. The EIS plot, ECSA, and TOF estimation disclose that the increased electrical conductivity, the improved ECSA, and the high intrinsic activity are together responsible for the good OER activity for 5%Ru-CoPO.(c) 2022 Elsevier Ltd. All rights reserved.

Lead-free halides with perovskite-related structures, such as the vacancy-ordered perovskite Cs3Bi2Br9, are of interest for photovoltaic and optoelectronic applications. We find that addition of SnBr2 to the solution-phase synthesis of Cs3Bi2Br9 leads to substitution of up to 7% of the Bi(III) ions by equal quantities of Sn(II) and Sn(IV). The nature of the substitutional defects was studied by X-ray diffraction, 133Cs and 119Sn solid state NMR, X-ray photoelectron spectroscopy and density functional theory calculations. The resulting mixed-valence compounds show intense visible and near infrared absorption due to intervalence charge transfer, as well as electronic transitions to and from localised Sn-based states within the band gap. Sn(II) and Sn(IV) defects preferentially occupy neighbouring B-cation sites, forming a double-substitution complex. Unusually for a Sn(II) compound, the material shows minimal changes in optical and structural properties after 12 months storage in air. Our calculations suggest the stabilisation of Sn(II) within the double substitution complex contributes to this unusual stability. These results expand upon research on inorganic mixed-valent halides to a new, layered structure, and offer insights into the tuning, doping mechanisms, and structure–property relationships of lead-free vacancy-ordered perovskite structures.

Metal nanoparticles on the surface of porous supports have found numerous applications in different areas of science. Fischer-Tropsch synthesis, which proceeds on the surface of cobalt metal nanoparticles, is an efficient way to convert renewables and fossil feedstocks into alternative fuels. The stability of cobalt catalysts is an essential and even crucial parameter and can be significantly improved by promotion. In this paper, a combination of operando Quick-XAS, NAP-XPS, high resolution electron microscopy imaging, DFT modeling alongside with Fischer-Tropsch catalytic experiments has provided deep insights into the evolution of bismuth promoter and structure of cobalt-bismuth nanoparticles in the catalysts supported by carbon nanotubes. We uncovered noticeable migration of metallic bismuth occurring during the reduction step, which leads to bismuth redispersion over the surface of cobalt nanoparticles. Cobalt reduction is facilitated in the presence of bismuth. The working Fischer-Tropsch catalyst contains cobalt-bismuth bimetallic nanoparticles, with bismuth located in the nanoparticle shell. The promotion with bismuth has resulted in a noticeable increase in catalyst stability. Characterization and DFT modeling suggest preferential localization of bismuth mobile promoter at the steps and edges of cobalt nanoparticles, which hinders cobalt sintering and carbon deposition and improves the catalyst stability.

We present evidence of homogenization of atomic diffusion properties caused by C and N interstitials in an equiatomic single-phase high entropy alloy (FeMnNiCoCr). This phenomenon is manifested by an unexpected interstitial-induced reduction and narrowing of the directly experimentally determined migration barrier distribution of mono-vacancy defects introduced by particle irradiation. Our observation by positron annihilation spectroscopy is explained by state-of-the-art theoretical calculations that predict preferential localization of C/N interstitials in regions rich in Mn and Cr, leading to a narrowing and reduction of the mono-vacancy size distribution in the random alloy. This phenomenon is likely to have a significant impact on the mechanical behavior under irradiation, as the local variations in elemental motion have a profound effect on the solute strengthening in high entropy alloys. (C) 2021 The Authors. Published by Elsevier Ltd on behalf of Acta Materialia Inc.

Interface diffusion along a metal/ceramic interface present in numerous energy and electronic devices can critically affect their performance and stability. Hole formation in a polycrystalline Ni film on an α-Al2O3 substrate coupled with a continuum diffusion analysis demonstrates that Ni diffusion along the Ni/α-Al2O3 interface is surprisingly fast. Ab initio calculations demonstrate that both Ni vacancy formation and migration energies at the coherent Ni/α-Al2O3 interface are much smaller than in bulk Ni, suggesting that the activation energy for diffusion along coherent Ni/α-Al2O3 interfaces is comparable to that along (incoherent/high angle) grain boundaries. Based on these results, we develop a simple model for diffusion along metal/ceramic interfaces, apply it to a wide range of metal/ceramic systems and validate it with several ab initio calculations. These results suggest that fast metal diffusion along metal/ceramic interfaces should be common, but is not universal., Little is known about diffusion along metal/ceramic interfaces even though it controls the physical behavior and lifetimes of many devices (including batteries, microelectronics, and jet engines). Here, the authors show that diffusion along a nickel/sapphire interface is abnormally fast due to nickel vacancies and generalise their findings to a wide-range of metal/ceramic systems.

In several domains of physics, including first principle simulations and classical models for polarizable systems, the minimization of an energy function with respect to a set of auxiliary variables must be performed to define the dynamics of physical degrees of freedom. In this paper, we discuss a recent algorithm proposed to efficiently and rigorously simulate this type of systems: the Mass-Zero (MaZe) Constrained Dynamics. In MaZe the minimum condition is imposed as a constraint on the auxiliary variables treated as degrees of freedom of zero inertia driven by the physical system. The method is formulated in the Lagrangian framework, enabling the properties of the approach to emerge naturally from a fully consistent dynamical and statistical viewpoint. We begin by presenting MaZe for typical minimization problems where the imposed constraints are holonomic and summarizing its key formal properties, notably the exact Born-Oppenheimer dynamics followed by the physical variables and the exact sampling of the corresponding physical probability density. We then generalize the approach to the case of conditions on the auxiliary variables that linearly involve their velocities. Such conditions occur, for example, when describing systems in external magnetic field and they require to adapt MaZe to integrate semiholonomic constraints. The new development is presented in the second part of this paper and illustrated via a proof-of-principle calculation of the charge transport properties of a simple classical polarizable model of NaCl., 21 pages, 7 figures

The computational discovery and design of zeolites is a crucial part of the chemical industry. Finding highly accurate while computationally feasible protocol for identification of hypothetical zeolites that could be targeted experimentally is a great challenge. To tackle the challenge, we trained neural network potentials (NNP) with the SchNet architecture on a structurally diverse database of density functional theory (DFT) data. This database was iteratively extended by active learning to cover not only low-energy equilibrium configurations but also high-energy transition states. We demonstrate that the resulting reactive NNPs retain the accuracy of the DFT reference for thermodynamic stabilities, vibrational properties, and reactive and non-reactive phase transformations. The novel NNPs outperforms specialized, analytical force fields for silica, such as ReaxFF, by order(s) of magnitude in accuracy, while speeding up the calculations in comparison to DFT by at least three orders of magnitude. As a showcase, we screened an existing zeolite database containing 330 thousand structures and revealed more than 20 thousand additional hypothetical frameworks in the thermodynamically accessible range of zeolite synthesis. Hence, our NNPs are expected to be essential for future high-throughput studies on the structure and reactivity of hypothetical and existing zeolites., Comment: This version of the article has been accepted for publication, after peer review (when applicable) but is not the Version of Record and does not reflect post-acceptance improvements, or any corrections. The Version of Record is available on line at: http://dx.doi.org/10.1038/s41524-022-00865-w

Simulations can be used to accelerate the characterization and discovery of materials. Here we Review how electronic-structure methods such as density functional theory work, what properties they can be used to predict and how they can be used to design materials., The accuracy and efficiency of electronic-structure methods to understand, predict and design the properties of materials has driven a new paradigm in research. Simulations can greatly accelerate the identification, characterization and optimization of materials, with this acceleration driven by continuous progress in theory, algorithms and hardware, and by adaptation of concepts and tools from computer science. Nevertheless, the capability to identify and characterize materials relies on the predictive accuracy of the underlying physical descriptions, and on the ability to capture the complexity of realistic systems. We provide here an overview of electronic-structure methods, of their application to the prediction of materials properties, and of the different strategies employed towards the broader goals of materials design and discovery.

ispartof: JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS vol:163 status: published

Metal borides have attracted the attention of researchers due to their useful physical properties and unique ability to form high hydrogen-capacity metal borohydrides. We demonstrate improved hydrogen storage properties of a nanoscale Mg-B material made by surfactant ball milling MgB2 in a mixture of heptane, oleic acid, and oleylamine. Transmission electron microscopy data show that Mg-B nanoplatelets are produced with sizes ranging from 5 to 50 nm, which agglomerate upon ethanol washing to produce an agglomerated nanoscale Mg-B material of micron-sized particles with some surfactant still remaining. X-ray diffraction measurements reveal a two-component material where 32% of the solid is a strained crystalline solid maintaining the hexagonal structure with the remainder being amorphous. Fourier transform infrared shows that the oleate binds in a "bridge-bonding"fashion preferentially to magnesium rather than boron, which is confirmed by density functional theory calculations. The Mg-B nanoscale material is deficient in boron relative to bulk MgB2 with a Mg-B ratio of ∼1:0.75. The nanoscale MgB0.75 material has a disrupted B-B ring network as indicated by X-ray absorption measurements. Hydrogenation experiments at 700 bar and 280 °C show that it partially hydrogenates at temperatures 100 °C below the threshold for bulk MgB2 hydrogenation. In addition, upon heating to 200 °C, the H-H bond-breaking ability increases ∼10-fold according to hydrogen-deuterium exchange experiments due to desorption of oleate at the surface. This behavior would make the nanoscale Mg-B material useful as an additive where rapid H-H bond breaking is needed.

We study the reactivity of Fe(IV)O moieties supported by a metal–organic framework (MOF-74) in the oxidation reaction of methane to methanol using all-electron, periodic density-functional theory calculations. We compare results concerning the electronic properties and reactivity obtained using two hybrid (B3LYP and sc-BLYP) and two standard generalised gradient corrected (PBE and BLYP) semi-local density functional approximations. The semi-local functionals are unable to reproduce the expected reaction profiles and yield a qualitatively incorrect representation of the reactivity. Non-local hybrid functionals provide a substantially more reliable description and predict relatively modest (ca. 60 kJ mol−1) reaction energy barriers for the H-atom abstraction reaction from CH4 molecules. We examine the origin of these differences and we highlight potential means to overcome the limitations of standard semi-local functionals in reactivity calculations in solid-state systems., This research was supported in part by the University of Pittsburgh Center for Research Computing through the resources provided and the Supercomputing Center of Galicia (CESGA), Spain.

The stability of metal-organic frameworks (MOFs) typically decreases with an increasing number of defects, limiting the number of defects that can be created and limiting catalytic and other applications. Herein, we use a hemilabile (Hl) linker to create up to a maximum of six defects per cluster in UiO-66. We synthesized hemilabile UiO-66 (Hl-UiO-66) using benzene dicarboxylate (BDC) as linker and 4-sulfonatobenzoate (PSBA) as the hemilabile linker. The PSBA acts not only as a modulator to create defects but also as a coligand that enhances the stability of the resulting defective framework. Furthermore, upon a postsynthetic treatment in H2SO4, the average number of defects increases to the optimum of six missing BDC linkers per cluster (three per formula unit), leaving the Zr-nodes on average sixfold coordinated. Remarkably, the thermal stability of the materials further increases upon this treatment. Periodic density functional theory calculations confirm that the hemilabile ligands strengthen this highly defective structure by several stabilizing interactions. Finally, the catalytic activity of the obtained materials is evaluated in the acid-catalyzed isomerization of α-pinene oxide. This reaction is particularly sensitive to the Brønsted or Lewis acid sites in the catalyst. In comparison to the pristine UiO-66, which mainly possesses Brønsted acid sites, the Hl-UiO-66 and the postsynthetically treated Hl-UiO-66 structures exhibited a higher Lewis acidity and an enhanced activity and selectivity. This is further explored by CD3CN spectroscopic sorption experiments. We have shown that by tuning the number of defects in UiO-66 using PSBA as the hemilabile linker, one can achieve highly defective and stable MOFs and easily control the Brønsted to Lewis acid ratio in the materials and thus their catalytic activity and selectivity. ispartof: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY vol:142 issue:6 pages:3174-3183 ispartof: location:United States status: published

The use of methane as one of the cleanest energy sources has attracted significant public awareness, and methane production processes with less environmental impact than fracking are receiving considerable attention. Catalytic hydrocracking of plastic materials has been considered a potential clean alternative. However, catalysts that convert heterogeneous plastic feeds into a single product under industrially relevant conditions are lacking. Here, we describe a Ru-modified zeolite that catalytically transforms polyethylene, polypropylene, and polystyrene into grid-compatible methane (>97% purity), at 300 degrees C-350 degrees C using near-stoichiometric amounts of H-2. Mechanistic studies reveal a chain-end initiation process with limited isomerization of plastic substrates. A Ru site-dominant mechanism is proposed based on these studies and density functional theory (DFT) computations. We foresee that such a plastic-to-methane process may increase the intelligent use of plastic waste via energy recovery. There is also the potential to accommodate emerging sustainable H-2 production into existing natural gas networks, while integrating waste management, fuel production, and energy storage.

Density functional theory (DFT) calculations are used to study the magnetic and ferroelectric properties of Sr 1 − x Ba x Mn O 3 , with focus on x = 0.5 , under isotropic volume expansion or compression and biaxial strain. Our results indicate that, unexpectedly, Ba substitution alters the electronic structure in a way that, at fixed lattice parameter, notably enhances the interatomic magnetic exchange interactions. However, increasing Ba content also causes a volume expansion which tends to weaken these interactions, leading to a net effect of weakly suppressed magnetism, as observed in experiments. The ferroelectric properties, on the other hand, are found to be less affected by changes in the electronic structure and can largely be understood in terms of the volume expansion caused by Ba substitution. The calculated electric polarization as a function of biaxial strain in Sr 1 − x Ba x Mn O 3 for x = 0 and x = 0.5 shows that the difference between the two is mainly due to differences in the magnetic order at certain strain values, accompanied by enormous magnetoelectric coupling., This work was supported by the Swiss National Science Foundation (Project Code No. 200021E-162297) and the German Science Foundation under the Priority Program No. SPP 1599 (“Ferroic Cooling”). Computational work was performed on resources provided by the Swiss National Supercomputing Centre (CSCS) and the ETH Zürich.

We present an overview of the onetep program for linear-scaling density functional theory (DFT) calculations with large basis set (plane-wave) accuracy on parallel computers. The DFT energy is computed from the density matrix, which is constructed from spatially localized orbitals we call Non-orthogonal Generalized Wannier Functions (NGWFs), expressed in terms of periodic sinc (psinc) functions. During the calculation, both the density matrix and the NGWFs are optimized with localization constraints. By taking advantage of localization, onetep is able to perform calculations including thousands of atoms with computational effort, which scales linearly with the number or atoms. The code has a large and diverse range of capabilities, explored in this paper, including different boundary conditions, various exchange-correlation functionals (with and without exact exchange), finite electronic temperature methods for metallic systems, methods for strongly correlated systems, molecular dynamics, vibrational calculations, time-dependent DFT, electronic transport, core loss spectroscopy, implicit solvation, quantum mechanical (QM)/molecular mechanical and QM-in-QM embedding, density of states calculations, distributed multipole analysis, and methods for partitioning charges and interactions between fragments. Calculations with onetep provide unique insights into large and complex systems that require an accurate atomic-level description, ranging from biomolecular to chemical, to materials, and to physical problems, as we show with a small selection of illustrative examples. onetep has always aimed to be at the cutting edge of method and software developments, and it serves as a platform for developing new methods of electronic structure simulation. We therefore conclude by describing some of the challenges and directions for its future developments and applications.

Recently, structural studies in the thin-film phase of 6,6′-dibromoindigo, the main component of the Tyrian purple dye, revealed the presence of surface-induced structures. This finding is important, as the system is a good candidate for applications in organic electronics, and knowledge of the film structure is needed to explain the physical properties of the conducting layer. In this work, combining the results of low-frequency Raman spectroscopy, X-ray diffraction, and accurate density-functional theory (DFT) calculations of the vibrational properties of the proposed surface-induced structures, we suggest that a newly detected 6,6′-dibromoindigo bulk crystal form is structurally closely related to the surface-induced modifications. Thus, 6,6′-dibromoindigo behavior shows similarities and differences at the same time, with respect to other investigated systems., We thank CINECA Supercomputing Center for providing computer time through the ISCRA scheme (project C—SCSCDFT). T.S. acknowledges the H2020-MSCA-COFUND-2014 Programme (P-SPHERE, Grant agreement 665919). The authors thank Prof. Roland Resel for the fruitful discussions. This work has been funded by the PRIN project “From natural to artificial light-harvesting systems: unveiling fundamental processes toward a bio-inspired materials design” (HARVEST) protocol 201795SBA3.

Over the past decades, investigations of the anomalous low-energy electronic properties of ZrTe$_5$ have reached a wide array of conclusions. An open question is the growth method's impact on the stoichiometry of ZrTe$_5$ samples, especially given the very small density of states near its chemical potential. Here we report on high resolution scanning tunneling microscopy and spectroscopy measurements performed on samples grown via different methods. Using density functional theory calculations, we identify the most prevalent types of atomic defects on the surface of ZrTe$_5$, namely Te vacancies and intercalated Zr atoms. Finally, we precisely quantify their density and outline their role as ionized defects in the anomalous resistivity of this material., Comment: 12 pages, 10 figures; Accepted for publication in Physical Review Materials

ispartof: Chemcatchem vol:12 issue:4 pages:1095-1108 status: published

Metal oxides can act as insulators, semiconductors or metals depending on their chemical composition and crystal structure. Metal oxide semiconductors, which support equilibrium populations of electron and hole charge carriers, have widespread applications including batteries, solar cells, and display technologies. It is often difficult to predict in advance whether these materials will exhibit localized or delocalized charge carriers upon oxidation or reduction. We combine data from first-principles calculations of the electronic structure and dielectric response of 214 metal oxides to predict the energetic driving force for carrier localization and transport. We assess descriptors based on the carrier effective mass, static polaron binding energy, and Frohlich electron–phonon coupling. Numerical analysis allows us to assign p and n type transport of a metal oxide to three classes: (i) band transport with high mobility; (ii) small polaron transport with low mobility; and (iii) intermediate behaviour. The results of this classification agree with observations regarding carrier dynamics and lifetimes and are used to predict 10 candidate p-type oxides.

Publisher's version (útgefin grein)., CO2 can be reduced electrochemically to form valuable chemicals such as hydrocarbons and alcohols using copper electrodes, whereas the other metal electrodes tested so far mainly form CO or formate, or only the side product, H2. Accurate modeling of electrochemical reaction rates including the complex environment of an electrical double layer in the presence of an applied electrical potential is challenging. We show here that calculated rates, obtained using a combination of density functional and rate theory, are in close agreement with available experimental data on the formation of the various products on several metal electrodes and over a range in applied potential, thus demonstrating the applicability of the theoretical methodology. The results explain why copper electrodes give a significant yield of hydrocarbons and alcohols, and why methane, ethylene, and ethanol are formed in electroreduction rather than methanol, which is the main product when H2 gas reacts with CO2 on copper catalyst. The insight obtained from the calculations is used to develop criteria for identifying new and improved catalysts for electrochemical CO2 reduction., We thank Marc Koper, Jens K. Nørskov, Andrew Peterson, Jan Rossmeisl and Anna Garden for helpful discussions. This work was supported by Nordic Energy Research through the “Nordic Initiative for Solar Fuel Development”, the Icelandic Research Fund, the University of Iceland Doctoral Scholarship Fund, and the Academy of Finland FiDiPro program (grant 263294).

Thin films of interstitial boron-doped anatase TiO2, with varying B concentrations, were deposited via one-step atmos-pheric pressure chemical vapour deposition (APCVD) on float glass substrates. The doped films showed a remarkable morphology and enhanced photoactivity when compared to their undoped analogues. The TiO2:B films also presented enhanced conductivity and electron mobility as measured by Hall Effect probe as well as a high adherence to the sub-strate, stability and extended lifetime. The structure and composition of the different samples of TiO2:B films were studied by X-ray Diffraction (XRD), Raman spectroscopy, Scanning Electron Microscopy (SEM) and Dynamic Second-ary Ion Mass Spectrometry (D-SIMS). Hybrid density functional theory was used to explore the defect chemistry of B-doped anatase and to understand the experimental results.

Alkali metal ion intercalation into layered transition-metal dichalcogenide structures is a promising approach to make next generation rechargeable batteries for energy storage. It has been noted that the number of Na-ions which can be reversibly intercalated and extracted per MoS2 is limited, and the chemical and electrochemical processes/mechanisms remain largely unknown, especially for nano-sized materials. Here, sodiation of MoS2 nanosheets are studied by in-situ electron diffraction and the phase transformations in sodiation are identified with the aid of DFT calculations to reveal the reaction mechanism. Several thermodynamically stable/metastable structures are identified in the sodiation pathway of MoS2 nanosheets, previously unnoticed in bulk MoS2. The gradual reduction of Mo4+ upon Na-ion intercalation leads to a transition of the Mo-S polyhedron from a trigonal prism to an octahedron around 0.375 Na per MoS2 inserted (i.e. Na0.375MoS2). When the intercalated Na-content is larger than 1.75 per MoS2 structural unit (i.e. Na1.75MoS2), the MoS2 layered structure collapses and the intercalation reaction is replaced by an irreversible conversion reaction with the formation of Na2S and metal Mo nanoparticles. The calculated sodiation pathways reproduce the experimental sodiation voltages. The current observations provide useful insights in developing sodium-ion batteries with high cycling stability.

One of the major requirements in solid acid and base catalyzed reactions is that the reactants, intermediates or activated complexes cooperate with several functions of catalyst support. In this work the remarkable bifunctional behavior of the defective UiO‐66(Zr) metal organic framework is shown for acid‐base pair catalysis. The active site relies on the presence of coordinatively unsaturated zirconium sites, which may be tuned by removing framework linkers and by removal of water from the inorganic bricks using a dehydration treatment. To elucidate the amphoteric nature of defective UiO‐66, the Oppenauer oxidation of primary alcohols has been theoretically investigated using density functional theory (DFT) and the periodic approach. The presence of acid and basic centers within molecular distances is shown to be crucial for determining the catalytic activity of the material. Hydrated and dehydrated bricks have a distinct influence on the acidity and basicity of the active sites. In any case both functions need to cooperate in a concerted way to enable the chemical transformation. Experimental results on UiO‐66 materials of different defectivity support the theoretical observations made in this work.

UiO-66 is a promising metal-organic framework for photocatalytic applications. However, the ligand-to-metal charge transfer of an excited electron is inefficient in the pristine material. Herein, we assess the influence of missing linker defects on the electronic structure of UiO-66 and discuss their ability to improve ligand-to-metal charge transfer. Using a new defect classification system, which is transparent and easily extendable, we identify the most promising photocatalysts by considering both relative stability and electronic structure. We find that the properties of UiO-66 defect structures largely depend on the coordination of the constituent nodes and that the nodes with the strongest local distortions alter the electronic structure most. Defects hence provide an alternative pathway to tune UiO-66 for photocatalytic purposes, besides linker modification and node metal substitution. In addition, the decomposition of MOF properties into node- and linker-based behavior is more generally valid, so we propose orthogonal electronic structure tuning as a paradigm in MOF design.

A recently developed finite element approach for fully numerical atomic structure calculations [S. Lehtola, Int. J. Quantum Chem. 119, e25945 (2019)] is extended to the description of atoms with spherically symmetric densities via fractionally occupied orbitals. Specialized versions of Hartree-Fock as well as local density and generalized gradient approximation density functionals are developed, allowing extremely rapid calculations at the basis set limit on the ground and low-lying excited states even for heavy atoms. The implementation of range-separation based on the Yukawa or complementary error function (erfc) kernels is also described, allowing complete basis set benchmarks of modern range-separated hybrid functionals with either integer or fractional occupation numbers. Finally, computation of atomic effective potentials at the local density or generalized gradient approximation levels for the superposition of atomic potentials (SAP) approach [S. Lehtola, J. Chem. Theory Comput. 15, 1593 (2019)] that has been shown to be a simple and efficient way to initialize electronic structure calculations is described. The present numerical approach is shown to afford beyond microhartree accuracy with a small number of numerical basis functions, and to reproduce literature results for the ground states of atoms and their cations for $1 \leq Z \leq 86 $. Our results indicate that the literature values deviate by up to 10 {\mu}Eh from the complete basis set limit. The numerical scheme for the erfc kernel is shown to work by comparison to results from large Gaussian basis set calculations from the literature. Spin-restricted ground states are reported for Hartree-Fock and Hartree-Fock-Slater calculations with fractional occupations for $1 \leq Z \leq 118$., Comment: 20 pages

Scientific reports 9(1), 7898 (2019). doi:10.1038/s41598-019-44326-9, Calcium carbonate is a relevant constituent of the Earth’s crust that is transferred into the deep Earth through the subduction process. Its chemical interaction with calcium-rich silicates at high temperatures give rise to the formation of mixed silicate-carbonate minerals, but the structural behavior of these phases under compression is not known. Here we report the existence of a dense polymorph of Ca$_5$(Si$_2$O$_7$)(CO$_3$)$_2$ tilleyite above 8 GPa. We have structurally characterized the two phases at high pressures and temperatures, determined their equations of state and analyzed the evolution of the polyhedral units under compression. This has been possible thanks to the agreement between our powder and single-crystal XRD experiments, Raman spectroscopy measurements and ab-initio simulations. The presence of multiple cation sites, with variable volume and coordination number (6–9) and different polyhedral compressibilities, together with the observation of significant amounts of alumina in compositions of some natural tilleyite assemblages, suggests that post-tilleyite structure has the potential to accommodate cations with different sizes and valencies, Published by Macmillan Publishers Limited, part of Springer Nature, [London]

Theory and experiment are combined to gain an understanding of the electronic properties of OsO2, a poorly studied metallic oxide that crystallizes in the rutile structure. Hard and soft valence-band x-ray photoemission spectra of OsO2 single crystals are in broad agreement with the results of density-functional-theory calculations, aside from a feature shifted to high binding energy of the conduction band. The energy shift corresponds to the conduction electron plasmon energy measured by reflection electron energy loss spectroscopy. The plasmon satellite is reproduced by many-body perturbation theory.