RESUMO
Advances in computational chemistry create an ongoing need for larger and higher-quality datasets that characterize noncovalent molecular interactions. We present three benchmark collections of quantum mechanical data, covering approximately 3,700 distinct types of interacting molecule pairs. The first collection, which we refer to as DES370K, contains interaction energies for more than 370,000 dimer geometries. These were computed using the coupled-cluster method with single, double, and perturbative triple excitations [CCSD(T)], which is widely regarded as the gold-standard method in electronic structure theory. Our second benchmark collection, a core representative subset of DES370K called DES15K, is intended for more computationally demanding applications of the data. Finally, DES5M, our third collection, comprises interaction energies for nearly 5,000,000 dimer geometries; these were calculated using SNS-MP2, a machine learning approach that provides results with accuracy comparable to that of our coupled-cluster training data. These datasets may prove useful in the development of density functionals, empirically corrected wavefunction-based approaches, semi-empirical methods, force fields, and models trained using machine learning methods.
RESUMO
The oxygen evolution reaction (OER) in alkaline media was investigated on nanostructured Fe2O3, NiO, and Ni1-xFexO (Fe-doped, rocksalt NiO, x = 0.05-0.19) electrocatalysts deposited via microplasma on indium tin oxide. A detailed investigation of film morphology, structure, and chemical surface state using SEM, XRD, and XPS, respectively, was carried out to understand catalytic activity, which was assessed using cyclic voltammetry and chronopotentiometry. Iron was seen to be fully incorporated into the parent rocksalt NiO lattice during microplasma deposition, and overpotentials (η) decreased from 360 mV for NiO to 310 mV for Ni1-xFexO at 10 mA cm-2. Interestingly, overpotential did not change significantly for Fe compositions from 5-19%. The Ni1-xFexO films displayed relatively low Tafel slopes of 20-30 mV dec-1 at 0.01-1 mA cm-2, demonstrating their high activity for (OER). Turn-over-frequency (TOF, i.e., O2 molecules per Ni atom per s) at η = 350 mV revealed a continuous improvement in activity of the NiO surface with increasing Fe content, where values of 0.07 and 0.48 s-1 were measured for undoped NiO and Ni0.81Fe0.19O films, respectively. Chronopotentiometry measurements followed by SEM and XPS verified that the as-deposited Ni1-xFexO catalysts were mechanically and chemically stable for OER under alkaline conditions. This work highlights that microplasma-based deposition is a general approach to realize conformal coatings of nanostructured, doped oxides with high activity for OER.
RESUMO
Micromechanical experiments, image analysis, and theoretical modeling revealed that local failure events and compressive stresses of vertically aligned carbon nanotubes (VACNTs) were uniquely linked to relative density gradients. Edge detection analysis of systematically obtained scanning electron micrographs was used to quantify a microstructural figure-of-merit related to relative local density along VACNT heights. Sequential bottom-to-top buckling and hardening in stress-strain response were observed in samples with smaller relative density at the bottom. When density gradient was insubstantial or reversed, bottom regions always buckled last, and a flat stress plateau was obtained. These findings were consistent with predictions of a 2D material model based on a viscoplastic solid with plastic non-normality and a hardening-softening-hardening plastic flow relation. The hardening slope in compression generated by the model was directly related to the stiffness gradient along the sample height, and hence to the local relative density. These results demonstrate that a microstructural figure-of-merit, the effective relative density, can be used to quantify and predict the mechanical response.
