PerQueue: managing complex and dynamic workflows.

Workflow managers play a critical role in the efficient planning and execution of complex workloads. A handful of these already exist within the world of computational materials discovery, but their dynamic capabilities are somewhat lacking. The PerQueue workflow manager is the answer to this need.

Understanding Pressure Effects on Structural, Optical, and Magnetic Properties of CsMnF and Other 3d Compounds.

The pressure dependence of structural, optical, and magnetic properties of the layered compound CsMnF are explored through first-principles calculations. The structure at ambient pressure does not arise from a Jahn-Teller effect but from an orthorhombic instability on MnF units in the tetragonal parent phase, while there is a 4/ → 4 structural phase transition at = 40 GPa discarding a spin crossover transition from = 2 to = 1. The present results reasonably explain the evolution of spin-allowed d-d transitions under pressure, showing that the first transition undergoes a red-shift under pressure following the orthorhombic distortion in the layer plane.

Electron-vibrational renormalization in fullerenes through and machine learning methods.

The effect of nuclear vibrations on the electronic eigenvalues and the HOMO-LUMO gap is known for several kinds of carbon-based materials, like diamond, diamondoids, carbon nanoclusters, carbon nanotubes and others, like hydrogen-terminated oligoynes and polyyne. However, it has not been widely analysed in another remarkable kind which presents both theoretical and technological interest: fullerenes. In this article we present the study of the HOMO, LUMO and gap renormalizations due to zero-point motion of a relatively large number (163) of fullerenes and fullerene derivatives.

Strain-Phonon Cooperation as a Necessary Ingredient to Understand the Jahn-Teller Effect in Solids.

Spatial degeneracy is the cause of the complex electronic, geometrical, and magnetic structures found in a number of materials whose more representative example is KCuF. In the literature the properties of this lattice are usually explained through the Kugel--Khomskii model, based on superexchange interactions. Here we provide rigorous theoretical and computational arguments against this view proving that structural and magnetic properties essentially arise from electron-vibration (vibronic) interactions.

Correction: Mechanisms of Electronic and Ionic Transport during Mg Intercalation in Mg-S Cathode Materials and Their Decomposition Products.

[This corrects the article DOI: 10.1021/acs.chemmater.

Prussian Blue Analogues as Positive Electrodes for Mg Batteries: Insights into Mg Intercalation.

Potassium manganese hexacianoferrate has been prepared by co-precipitation from manganese (II) chloride and potassium citrate, with chemical analysis yielding the formula K Mn[Fe(CN) ] □  ⋅ 1.1H O (KMnHCF). Its X-ray diffraction pattern is consistent with a monoclinic structure (space group P 2 /n, no.

Electrolytes for Zn Batteries: Deep Eutectic Solvents in Polymer Gels.

Gel polymer electrolytes composed of deep eutectic solvent acetamide :Zn(TFSI) and poly(ethylene oxide) (PEO) are prepared by using a fast, solvent-free procedure. The effect of the PEO molecular weight and its concentration on the physicochemical and electrochemical properties of the electrolytes are studied. Gels prepared with ultrahigh molecular-weight PEO present pseudo-solid behavior and ionic conductivity even higher than that of the original liquid electrolyte.

Red Shift in Optical Excitations on Layered Copper Perovskites under Pressure: Role of the Orthorhombic Instability.

The red shift under pressure in optical transitions of layered compounds with CuCl units is explored through first-principles calculations and the analysis of available experimental data. The results on Cu -doped (C H NH ) CdCl , that is taken as a guide, show the existence of a highly anisotropic response to pressure related to a structural instability, driven by a negative force constant, that leads to an orthorhombic geometry of CuCl units but with a hole displaying a dominant 3z -r character (z being the direction perpendicular to the layer plane). As a result of such an instability, a pressure of only 3 GPa reduces by 0.

Pressure Effects on 3d (n=4, 9) Insulating Compounds: Long Axis Switch in Na MnF not Due to the Jahn-Teller Effect.

The pressure-induced switch of the long axis of MnF units in the monoclinic Na MnF compound and Mn -doped Na FeF is explored with the help of first principles calculations. Although the switch phenomenon is usually related to the Jahn-Teller effect, we show that, due to symmetry reasons, it cannot take place in 3d (n=4, 9) systems displaying a static Jahn-Teller effect. By contrast, we prove that in Na MnF the switch arises from the anisotropic response of the low symmetry lattice to hydrostatic pressure.

Modeling of Electron-Transfer Kinetics in Magnesium Electrolytes: Influence of the Solvent on the Battery Performance.

The performance of rechargeable magnesium batteries is strongly dependent on the choice of electrolyte. The desolvation of multivalent cations usually goes along with high energy barriers, which can have a crucial impact on the plating reaction. This can lead to significantly higher overpotentials for magnesium deposition compared to magnesium dissolution.

Ab initio Molecular Dynamics Investigations of the Speciation and Reactivity of Deep Eutectic Electrolytes in Aluminum Batteries.

Invited for this month's cover is the Section for Atomic Scale Materials Modelling led by Prof. Tejs Vegge at the Department of Energy Conversion and Storage, Technical University of Denmark. The central image of the cover picture illustrates one of the chemical reaction mechanisms observed in a deep eutectic electrolyte formed by AlCl and urea.

Ab initio Molecular Dynamics Investigations of the Speciation and Reactivity of Deep Eutectic Electrolytes in Aluminum Batteries.

Deep eutectic solvents (DESs) have emerged as an alternative for conventional ionic liquids in aluminum batteries. Elucidating DESs composition is fundamental to understand aluminum electrodeposition in the battery anode. Despite numerous experimental efforts, the speciation of these DESs remains elusive.

Understanding the Molecular Structure of the Elastic and Thermoreversible AlCl : Urea/Polyethylene Oxide Gel Electrolyte.

It is possible to prepare elastic and thermoreversible gel electrolytes with significant electroactivity by dissolving minimal weight fractions of ultra-high molecular weight polyethylene oxide (UHMW PEO) in an aluminum deep eutectic solvent (DES) electrolyte composed of AlCl and urea at a molar ratio of 1.5 : 1 (AlCl /urea). The experimental vibrational spectra (FTIR and Raman) provide valuable information on the structure and composition of the gel electrolyte.

Modeling of Ion Agglomeration in Magnesium Electrolytes and its Impacts on Battery Performance.

The choice of electrolyte has a crucial influence on the performance of rechargeable magnesium batteries. In multivalent electrolytes an agglomeration of ions to pairs or bigger clusters may affect the transport in the electrolyte and the reaction at the electrodes. In this work the formation of clusters is included in a general model for magnesium batteries.

Correction: Density functional theory study of superoxide ions as impurities in alkali halides.

Correction for 'Density functional theory study of superoxide ions as impurities in alkali halides' by Alexander S. Tygesen et al., Phys.

Density functional theory study of superoxide ions as impurities in alkali halides.

The orientation of diatomic molecular impurities in crystals is a classic problem in physics, whose analysis started in the early 1930s with Pauling's pioneering studies and has extended to the present day. In the present work, we investigate the orientation of a superoxide ion (O2-), which is known to be oriented in the 1 1 0 direction when replacing a halide ion in alkali halide rock salt lattices. The unpaired electron of the superoxide, whose ground state is degenerate (2Πg), is oriented in the 0 0 1 direction for sodium halides while it is oriented in the 1 1[combining macron] 0 direction for potassium and rubidium halides.

The effect of CO contamination in rechargeable non-aqueous sodium-air batteries.

Metal-air batteries have higher theoretical specific energies than existing rechargeable batteries including Li-ion batteries. Among metal-air batteries, the Na-O battery has gained much attention due to its low discharge/charge overpotentials (∼100 mV) at relatively high current densities (0.2 mA/cm), high electrical energy efficiency (90%), high theoretical energy density, and low cost.

CLEASE: a versatile and user-friendly implementation of cluster expansion method.

Materials exhibiting a substitutional disorder such as multicomponent alloys and mixed metal oxides/oxyfluorides are of great importance in many scientific and technological sectors. Disordered materials constitute an overwhelmingly large configurational space, which makes it practically impossible to be explored manually using first-principles calculations such as density functional theory due to the high computational costs. Consequently, the use of methods such as cluster expansion (CE) is vital in enhancing our understanding of the disordered materials.

R-NEB: Accelerated Nudged Elastic Band Calculations by Use of Reflection Symmetry.

Many activated processes in materials science, physics, and chemistry, e.g. diffusion processes, have initial and final states related by symmetry.

Thermodynamic and Kinetic Limitations for Peroxide and Superoxide Formation in Na-O Batteries.

The Na-O system holds great potential as a low-cost, high-energy-density battery, but under normal operating conditions, the discharge is limited to sodium superoxide (NaO), whereas the high-capacity peroxide state (NaO) remains elusive. Here, we apply density functional theory calculations with an improved error-correction scheme to determine equilibrium potentials and free energies as a function of temperature for the different phases of NaO and NaO, identifying NaO as the thermodynamically preferred discharge product up to ∼120 K, after which NaO is thermodynamically preferred. We also investigate the reaction mechanisms and resulting electrochemical overpotentials on stepped surfaces of the NaO and NaO systems, showing low overpotentials for NaO formation (η = 0.

Machine learning-based screening of complex molecules for polymer solar cells.

Polymer solar cells admit numerous potential advantages including low energy payback time and scalable high-speed manufacturing, but the power conversion efficiency is currently lower than for their inorganic counterparts. In a Phenyl-C_61-Butyric-Acid-Methyl-Ester (PCBM)-based blended polymer solar cell, the optical gap of the polymer and the energetic alignment of the lowest unoccupied molecular orbital (LUMO) of the polymer and the PCBM are crucial for the device efficiency. Searching for new and better materials for polymer solar cells is a computationally costly affair using density functional theory (DFT) calculations.

Combined DFT and Differential Electrochemical Mass Spectrometry Investigation of the Effect of Dopants in Secondary Zinc-Air Batteries.

Zinc-air batteries offer the potential of low-cost energy storage with high specific energy, but at present secondary Zn-air batteries suffer from poor cyclability. To develop economically viable secondary Zn-air batteries, several properties need to be improved: choking of the cathode, catalyzing the oxygen evolution and reduction reactions, limiting dendrite formation and suppressing the hydrogen evolution reaction (HER). Understanding and alleviating HER at the negative electrode in a secondary Zn-air battery is a substantial challenge, for which it is necessary to combine computational and experimental research.

Large Differences in the Optical Spectrum Associated with the Same Complex: The Effect of the Anisotropy of the Embedding Lattice.

Transition-metal complexes with a well-defined geometry are usually considered to display almost the same properties independently of the system where they are embedded. Here we show that the above statement is not true depending on the anisotropy of the host lattice, which is revealed in the form of the electric field created by the rest of lattice ions over the complex. To illustrate this concept we analyze the origin of the surprisingly large differences in the d-d optical transitions of two systems containing square-planar CuF complexes, CaCuF, and center II in Cu-doped BaZnF, even though the Cu-Fdistance difference is just found to be 1%.

How covalence breaks adsorption-energy scaling relations and solvation restores them.

It is known that breaking the scaling relations between the adsorption energies of *O, *OH, and *OOH is paramount in catalyzing more efficiently the reduction of O in fuel cells and its evolution in electrolyzers. Taking metalloporphyrins as a case study, we evaluate here the adsorption energies of those adsorbates on the metal centers Cr, Mn, Fe, Co, Ni and Cu, using H, F, OH, NH, CH, and BH as ring ligands. We show that covalence systematically breaks scaling relations under vacuum by strengthening certain M-OOH bonds.