AndreaBozzo/ceres-open-data-index huggingface dataset:
Designing bifunctional perovskite catalysts for the oxygen reduction and evolution reactions

The development of unified regenerative fuel cells (URFC) necessitates an active and stable bifunctional oxygen electrocatalyst. The unique challenge of possessing high activity for both the oxygen reduction (ORR) and oxygen evolution (OER) reactions, while maintaining stability over a wide potential window impedes the design of bifunctional oxygen electrocatalysts. Herein, two design strategies are explored to optimize their performance. The first incorporates active sites for ORR and OER, Mn and Co, into a single perovskite structure, which is achieved with the perovskites Ba0.5Sr0.5Co0.8Mn0.2O3-δ (BSCM) and La0.5Ba0.25Sr0.25Co0.5Mn0.5O3-δ (LBSCM). The second combines an active ORR perovskite catalyst (La0.4Sr0.6MnO3-δ (LSM)) with an OER active perovskite catalyst (Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF)) in a physical mixed composite (BSCF/LSM). The success of the two strategies is investigated by measuring the catalysts' catalytic performance and response to alternating reducing and oxidizing potentials to mimic the dynamic conditions experienced during operation of URFCs. Additionally, the continuous, potentiodynamic change in Mn, Co, and Fe oxidation state during ORR and OER is elucidated with operando X-ray absorption spectroscopy (XAS) measurements, revealing key insights into the nature of the active sites. The results reveal important catalyst physiochemical properties and provide a guide for future research and design principles for bifunctional oxygen electrocatalysts.

Tags: oer, orr, perovskite
Calculation of screened Coulomb interaction parameters for the charge-disproportionated insulator CaFeO₃

We calculate the screened electron-electron interaction for the charge-disproportionated insulator CaFeO₃ using the constrained random-phase approximation (cRPA). While in many correlated materials, the formation of a Mott-insulating state is driven by a large local Coulomb repulsion, represented by the Hubbard U, several cases have been identified more recently where U is strongly screened and instead the Hund's interaction J dominates the physics. Our results confirm a strong screening of the local Coulomb repulsion U in CaFeO₃ whereas J is much less screened and can thus stabilize a charge-disproportionated insulating state. This is consistent with the case of the rare-earth nickelates where similar behavior has been demonstrated. In addition, we validate some common assumptions used for parametrizing the local electron-electron interaction in first-principles calculations based on density-functional theory (DFT), assess the dependence of the interaction on the choice of correlated orbitals, and discuss the use of the calculated interaction parameters in DFT+U calculations of CaFeO₃. Our work also highlights certain limitations for the direct use of cRPA results in DFT-based first-principles calculations, in particular for systems with strong entanglement between the correlated and uncorrelated bands.

Tags: charge-disproportionation, constrained-random-phase-approximation, metal-insulator-transition, perovskite
Reduction of precious metal ions in aqueous solutions by contact-electro-catalysis

Contact-Electro-Catalysis is an emerging catalytic principle that takes advantage of exchanges of electrons occurring through contact electrification events at solid-liquid interfaces to initiate or drive the catalysis of redox reactions. In this publication, the authors have proven the ability of various polymer insulators to catalyze the reduction of a wide variety of metal ions in aqueous solution, in both aerobic and anaerobic conditions. This property of the dielectric polymers was employed to design a 1-step method to selectively extract gold from e-waste leachates. In anaerobic conditions, the rate of the reactions increase due to the absence of competition form oxygen for the electrons. The influence of metal ions in solution on the distance between O₂ and the polymer chain of polytetrafluoroethylene was evaluated, as well as the resulting adsorption energy. The effect of tacticity on the ability of polymers such as PP to perform the contact-electro-catalytic reduction of oxygen was also evaluated. The files in this repository contains the position of the atoms before and after relaxation in all cases that were used to conduct the calculations.

Tags: catalysis, contact-electrification, contact-electro-catalysis, vasp
Charge state-dependent symmetry breaking of atomic defects in transition metal dichalcogenides

The functionality of atomic quantum emitters is intrinsically linked to their host lattice coordination. Structural distortions that spontaneously break the lattice symmetry strongly impact their optical emission properties and spin-photon interface. In a recent manuscript, we report on the direct imaging of charge state-dependent symmetry breaking of two prototypical atomic quantum emitters in mono- and bilayer MoS₂ by scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM). By changing the built-in substrate chemical potential, different charge states of sulfur vacancies (VacS) and substitutional rhenium dopants (ReMo) can be stabilized. VacS⁻¹ as well as ReMo⁰ and ReMo⁻¹ exhibit local lattice distortions and symmetry-broken defect orbitals attributed to a Jahn-Teller effect (JTE) and pseudo-JTE, respectively. By mapping the electronic and geometric structure of single point defects, we disentangle the effects of spatial averaging, charge multistability, configurational dynamics, and external perturbations that often mask the presence of local symmetry breaking. This record contains data to support the results discussed in our manuscript.

Tags: 2d-materials, dfg, erc, jahn-teller-effect, snsf, stm
Deterministic grayscale nanotopography to engineer mobilities in strained MoS₂ FETs

Field-effect transistors (FETs) based on two-dimensional materials (2DMs) with atomically thin channels have emerged as a promising platform for beyond-silicon electronics. However, low carrier mobility in 2DM transistors driven by phonon scattering remains a critical challenge. To address this issue, we propose the controlled introduction of localized tensile strain as an effective mean to inhibit electron-phonon scattering in 2DM. Strain is achieved by conformally adhering the 2DM via van-der-Waals forces to a dielectric layer previously nanoengineered with a gray-tone topography. Our results show that monolayer MoS₂ FETs under tensile strain achieve an 8-fold increase in on-state current, reaching mobilities of 185 cm²/Vs at room temperature, in good agreement with theoretical calculations. The present work on nanotopographic grayscale surface engineering and the use of high-quality dielectric materials has the potential to find application in the nanofabrication of photonic and nanoelectronic devices. Here we report the main data and codes needed to reproduce the theoretical findings of this work.

Tags: 2d-materials, density-functional-theory, electron-phonon-coupling, first-principles, transport
Explicit demonstration of the equivalence between DFT+U and the Hartree-Fock limit of DFT+DMFT

Several methods have been developed to improve the predictions of density functional theory (DFT) in the case of strongly correlated electron systems. Out of these approaches, DFT+U, which corresponds to a static treatment of the local interaction, and DFT combined with dynamical mean field theory (DFT+DMFT), which considers local fluctuations, have both proven incredibly valuable in tackling the description of materials with strong local electron-electron interactions. While it is in principle known that the Hartree-Fock (HF) limit of the DFT+DMFT approach should recover DFT+U, demonstrating this equivalence in practice is challenging, due to the very different ways in which the two approaches are generally implemented. In this work, we introduce a way to perform DFT+U calculations in QE using Wannier functions as calculated by Wannier90, which allows us to use the same Hubbard projector functions both in DFT+U and in DFT+DMFT. We benchmark these DFT+U calculations against DFT+DMFT calculations where the DMFT impurity problem is solved within the HF approximation. Considering a number of prototypical materials including NiO, MnO, LaMnO₃, and LuNiO₃, we establish the sameness of the two approaches. Finally, we showcase the versatility of our approach by going beyond the commonly used atomic orbital-like projectors by performing DFT+U calculations for VO₂ using a special set of bond-centered Wannier functions.

Tags: dftdmft, dftu, hartree-fock, marvel
A variational formulation of the Harris functional as correction to linear-scaling subsystem density functional theory

Accurate descriptions of intermolecular interactions are of great importance in simulations of molecular liquids. We present a novel method that combines in a variational formulation the accuracy of the Harris functional approach with the computational efficiency of linear-scaling subsystem density functional theory (DFT). While subsystem DFT methods allow for efficient large-scale simulations, they often lack in accuracy. The proposed method allows for simulations with millihartree accuracy in comparison to the Kohn-Sham DFT reference, at near linear-scaling efficiency. Embedded in the CP2K program package, the method is designed to enable ab initio molecular dynamics simulations of molecular solutions for system sizes of several thousands of atoms. As example of production applications we applied the method to molecular dynamics simulations in the isobaric-isothermal ensemble of the binary mixtures cyclohexane-methanol and toluene-methanol at different molar fractions of methanol. This record contains all CP2K input files necessary for the MD simulations, as well as 30ps trajectory files.

Tags: cp2k, cyclohexane, harris-functional, isobaric-isothermal-ensemble, linear-scaling-dft, methanol, molecular-dynamics-simulation, snsf, subsystem-dft, toluene
Preferential graphitic-nitrogen formation in pyridine-extended graphene nanoribbons

Graphene nanoribbons (GNRs), nanometer-wide strips of graphene, have garnered significant attention due to their tunable electronic and magnetic properties arising from quantum confinement. A promising approach to manipulate their electronic characteristics involves substituting carbon with heteroatoms, such as nitrogen, with different effects predicted depending on their position. In a recent publication, we present the extension of the edges of 7-atom-wide armchair graphene nanoribbons (7-AGNRs) with pyridine rings, achieved on a Au(111) surface via on-surface synthesis. High-resolution structural characterization confirms the targeted structure, showcasing the pre-dominant formation of carbon-nitrogen (C-N) bonds (over 90% of the units) during growth. This favored bond formation pathway is elucidated and confirmed through density functional theory (DFT) simulations. Furthermore, an analysis of the electronic properties reveals a reduction of the band gap of the GNR, accompanied by the presence of nitrogen-localized states. Our results underscore the successful formation of C-N bonds on the metal surface, providing insights for designing new GNRs that incorporate substitutional nitrogen atoms to precisely control their electronic properties. The record contains data that support the findings described in the publication.

Tags: aiidalab, cscs, dft, graphene-nanoribbons, marvelp4, nitrogen-doping, stm
A variational formulation of the Harris functional as correction to approximate Kohn-Sham density functional theory

Accurate descriptions of intermolecular interactions are of great importance in simulations of molecular liquids. We present an electronic structure method that combines the accuracy of the Harris functional approach with the computational efficiency of approximately linear-scaling density functional theory (DFT). The proposed method allows for simulations with accuracies close to the Kohn-Sham DFT reference. Embedded in the CP2K program package, the method is designed to enable ab initio molecular dynamics simulations of molecular solutions for system sizes of several thousands of atoms. As example of production applications we applied the method to molecular dynamics simulations in the isobaric-isothermal ensemble of the binary mixtures cyclohexane-methanol and toluene-methanol at different molar fractions of methanol. This record contains all CP2K input files necessary for the MD simulations, as well as 30ps trajectory files, and benchmark data of the energy correction.

Tags: cp2k, cyclohexane, harris-functional, isobaric-isothermal-ensemble, linear-scaling-dft, methanol, molecular-dynamics-simulation, s66x10, snsf, subsystem-dft, toluene
Curves data of a simple implicit method for parameters estimation of multi-junction solar cells

Multi-junction solar cells pose a particular modeling challenge, and advanced methods are needed to improve their efficiency and reduce their cost. We present here data about the I-V and P-V characteristics gotten using the electrical parameters obtained through an easy method to extract the electrical parameters of multi-junction solar cells using a single-diode model. The proposed technique is based solely on manufacturer data, and we solve the necessary mathematical equations numerically.

Tags: iv, multiple-junction, parameter-extraction-methods, solar-energy
Machine learning guided high-throughput search of non-oxide garnets

Garnets, known since the early stages of human civilization, have found important applications in modern technologies including magnetorestriction, spintronics, lithium batteries, etc. The overwhelming majority of experimentally known garnets are oxides, while explorations (experimental or theoretical) for the rest of the chemical space have been limited in scope.  A key issue is that the garnet structure has a large primitive unit cell, requiring an enormous amount of computational resources. To perform a comprehensive search of the complete chemical space for new garnets, we combine recent progress in graph neural networks with high-throughput calculations. We apply the machine learning model to identify the potential (meta-)stable garnet systems before systematic density-functional calculations to validate the predictions. In this way, we discover more than 600 ternary garnets with distances to the convex hull below 100~meV/atom with a variety of physical and chemical properties. This includes sulfide, nitride and halide garnets. This record includes the results of 15742 vasp calculations of the ternary garnets investigated. All calculations were performed using the PBE functional.

Tags: density-functional-theory, garnets, vasp
Polaron hopping through piecewise-linear functionals

We use piecewise-linear functionals to study the polaron energy landscape and hopping rates in 𝜷-Ga₂O₃, which we adopt as an example of an anisotropic material hosting multiple polaronic states. We illustrate various functionals for polaron localization, including a hybrid functional and two types of semilocal functionals, and discuss how to ensure the piecewise linearity condition. Then, we determine the formation energies of stable polarons, and show that single-site and multi-site polaronic states can be found in close energetic competition. We calculate the hyperfine and superhyperfine parameters associated with each polaron, and discuss the comparison with experiment. Next, we perform nudged-elastic-band calculations to determine energy landscapes and hole transfer rates of all first-nearest-neighbor polaron hoppings. We show that when the piecewise linearity condition is ensured polaron properties are robust upon variation of the functional adopted, including formation energies, energy barriers, and charge transfer rates. This supports the use of semilocal functionals for calculating polaron transport properties.

Tags: density-functional-theory, dftu, gammadft, hybrid-functionals, piecewise-linearity, polaron-hopping, polarons, self-interaction
Tunable topological Dirac surface states and van Hove singularities in kagome metal GdV6Sn6

Transition-metal-based kagome materials at van Hove filling are a rich frontier for the investigation of novel topological electronic states and correlated phenomena. To date, in the idealized two-dimensional kagome lattice, topologically Dirac surface states (TDSSs) have not been unambiguously observed, and the manipulation of TDSSs and van Hove singularities (VHSs) remains largely unexplored. Here, we reveal TDSSs originating from a Z2 bulk topology and identify multiple VHSs near the Fermi level (EF) in magnetic kagome material GdV6Sn6. Using in situ surface potassium deposition, we successfully realize manipulation of the TDSSs and VHSs. The Dirac point of the TDSSs can be tuned from above to below EF, which reverses the chirality of the spin texture at the Fermi surface. These results establish GdV6Sn6 as a fascinating platform for studying the nontrivial topology, magnetism, and correlation effects native to kagome lattices. They also suggest potential application of spintronic devices based on kagome materials.

Tags: arpesdft, kagome-metal-gdv6sn6, nccr-marvel, sino-swiss-science-and-technology-cooperation, tdsss-and-vhss
Dataset of proximity induced superconductivity in a topological insulator

Interfacing a topological insulator (TI) with an s-wave superconductor (SC) is a promising material platform that offers the possibility to realize a topological superconductor through which Majorana-based topologically protected qubits can be engineered. In our computational study of the prototypical SC/TI interface between Nb and Bi₂Te₃, we identify the benefits and possible bottlenecks of this potential Majorana material platform. Bringing Nb in contact with the TI film induces charge doping from the SC to the TI, which shifts the Fermi level into the TI conduction band. For thick TI films, this results in band bending leading to the population of trivial TI quantum-well states at the interface. In the superconducting state, we uncover that the topological surface state experiences a sizable superconducting gap-opening at the SC/TI interface, which is furthermore robust against fluctuations of the Fermi energy. We also show that the trivial interface state is only marginally proximitized, potentially obstructing the realization of Majorana-based qubits in this material platform.
This dataset contains the data for the DFT-based calculations for interfaces between the s-wave superconductor Nb and the topological insulator Bi₂Te₃ which is discussed in the publication referenced below.

Tags: bogoliubov-de-gennes, density-functional-theory, superconductivity, topological-materials, topological-superconductor
A machine learning model of chemical shifts for chemically and structurally diverse molecular solids

Nuclear magnetic resonance (NMR) chemical shifts are a direct probe of local atomic environments and can be used to determine the structure of solid materials. However, the substantial computational cost required to predict accurate chemical shifts is a key bottleneck for NMR crystallography. We recently introduced ShiftML, a machine-learning model of chemical shifts in molecular solids, trained on minimum-energy geometries of materials composed of C, H, N, O, and S that provides rapid chemical shift predictions with density functional theory (DFT) accuracy. Here, we extend the capabilities of ShiftML to predict chemical shifts for both finite temperature structures and more chemically diverse compounds, while retaining the same speed and accuracy. For a benchmark set of 13 molecular solids, we find a root-mean-squared error of 0.47 ppm with respect to experiment for 1H shift predictions (compared to 0.35 ppm for explicit DFT calculations), while reducing the computational cost by over four orders of magnitude.

Tags: machine-learning, marveldd1, snsf
Capturing dichotomic solvent behavior in solute–solvent reactions with neural network potentials

Simulations of chemical reactivity in condensed phase systems represent an ongoing challenge in computational chemistry, where traditional quantum chemical approaches typically struggle with both the size of the system and the potential complexity of the reaction. Here, we introduce a workflow aimed at efficiently training neural network potentials (NNPs) to explore energy barriers in solution at the hybrid density functional theory level. The computational burden associated with training at the PBE0-D3(BJ) level is bypassed through the use of active and transfer learning techniques, whereas extensive sampling of the transition state region is accelerated by well-tempered metadynamics simulations using multiple time-step integration. These NNPs serve to explore a puzzling solute--solvent reactivity route involving the ring opening of N-enoxyphthalimide experimentally observed in methanol but not in 2,2,2-trifluoroethanol (TFE). This reaction represents a challenging example characterized by intricate hydrogen bonding networks and structurally ambiguous solvent-sensitive transition states. The methodology successfully delivers detailed free energy surfaces and relative energy barriers in quantitative agreement with experiment. These barriers are associated with an ensemble of transition states involving direct participation of up to five solvent molecules. While this picture contrasts with the single transition state structure assumed by current static models, no drastic qualitative difference is observed between the formed hydrogen bonding networks and the number of participating solvent molecules in methanol or TFE. The dichotomy between the two solvents thus essentially arises from an electronic effect (i.e., distinct nucleophilicity) and from the larger conformational entropy contributions in methanol. This example  underscores the critical role dynamic simulations at the ab initio levels play in capturing the full complexity of solute-solvent interactions.

The files used in our studies are listed below, ensuring reproducibility and providing resources for future studies related to this work.

Tags: erc, free-energy, machine-learning, molecular-dynamics-simulation
Single in-situ interface characterization composed of niobium and a selectively grown topological insulator nanoribbon

With increasing interest in Majorana physics for possible quantum bit applications, a large interest has been developed to understand the properties of the interface between a s-type superconductor and a topological insulator. Up to this point the interface analysis was mainly focused on in-situ prepared Josephson junctions, which consist of two coupled single interfaces or to ex-situ fabricated single interface devices. In our work we utilize a novel fabrication process, combining selective area growth and shadow evaporation which allows the characterization of a single in-situ fabricated Nb/(Bi0.15Sb0.85)2Te3 nano interface. The resulting high interface transparency, is apparent by a zero bias conductance increase by a factor of 1.7. Furthermore, we present a comprehensive differential conductance analysis of our single in-situ interface for various magnetic fields, temperatures and gate voltages. Additionally, density functional theory calculations of the superconductor/topological insulator interface are performed in order to explain the peak-like shape of our differential conductance spectra and the origin of the observed smearing of conductance features.

This dataset contains the DFT and experimental raw data discussed in the associated publication.

Tags: density-functional-theory, experiment, majorana, superconductivity, topological-materials, topological-superconductor, transport