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Y-doped BaZrO 3 is a promising proton conductor for intermediate temperature solid oxide fuel cells. In this work, a combination of static DFT calculations and DFT based molecular dynamics (DFT-MD) was used to study proton conduction in this material. Geometry optimizations of 100 structures with a 12.5% dopant concentration allowed us to identify a clear correlation between the bending of the metal-oxygen-metal angle and the energies of the simulated cells. Depending on the type of bending, two configurations, designated as inward bending and outward bending, were defined. The results demonstrate that a larger bending decreases the energy and that the lowest energies are observed for structures combining inward bending with protons being close to the dopant atoms. These lowest energy structures are the ones with the strongest hydrogen bonds. DFT-MD simulations in cells with different yttrium distributions provide complementary microscopic information on proton diffusion as they capture the dynamic distortions of the lattice caused by thermal motion. A careful analysis of the proton jumps between different environments confirmed that the inward and outward bending states are relevant for the understanding of proton diffusion. Indeed, intra-octahedral jumps were shown to only occur starting from an outward configuration while the inward configuration seems to favor rotations around the oxygen. On average, in the DFT-MD simulations, the hydrogen bond lengths are shorter for the outward configuration which facilitates the intra-octahedral jumps. Diffusion coefficients and activation energies were also determined and compared to previous theoretical and experimental data, showing a good agreement with previous data measuring local proton motion., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

Disordered nanoporous and "hard" carbons are widely used in batteries and supercapacitors, but their atomic structures are poorly determined. Here, we combine machine learning and DFT to obtain new atomistic insight into carbonaceous energy materials. We study structural models of porous and graphitic carbons, and Na intercalation as relevant for sodium-ion batteries.

We have used molecular simulation and methods of importance sampling to study the thermodynamics and kinetics of ionic charge separation at a liquid water-metal interface. We have considered this process using canonical examples of two different classes of ions: a simple alkali-halide pair, Na + I - , or classical ions, and the products of water autoionization, H 3 O + OH - , or water ions. We find that for both ion classes, the microscopic mechanism of charge separation, including water's collective role in the process, is conserved between the bulk liquid and the electrode interface. However, the thermodynamic and kinetic details of the process differ between these two environments in a way that depends on ion type. In the case of the classical ion pairs, a higher free-energy barrier to charge separation and a smaller flux over that barrier at the interface result in a rate of dissociation that is 40 times slower relative to the bulk. For water ions, a slightly higher free-energy barrier is offset by a higher flux over the barrier from longer lived hydrogen-bonding patterns at the interface, resulting in a rate of association that is similar both at and away from the interface. We find that these differences in rates and stabilities of charge separation are due to the altered ability of water to solvate and reorganize in the vicinity of the metal interface., Competing Interests: The authors declare no conflict of interest.

The high overpotential in water oxidation on anodes is a limiting factor for the large-scale application of photoelectrochemical cells. To overcome this limitation, it is essential to understand the four proton-coupled electron transfer (PCET) steps in the reaction mechanism and their implications to the overpotential. Herein, a simple scheme to compute the energies of the PCET steps in water oxidation on the aqueous TiO2 surface using a hybrid density functional is described. An energy level diagram for fully decoupled electron- and proton-transfer reactions in which both electronic and protonic levels are placed on the same potential scale is also described. The level diagram helps to visualize the electronic and protonic components of the overpotential, and points out what are needed to improve. For TiO2, it is found that its catalytic activity is due to aligning the protonic energy levels in the PCET steps, while improving the activity requires also aligning the electronic levels., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The influence of the optimized effective potential (OEP) and Coulomb-attenuation on shielding constants and chemical shifts is investigated for three disparate categories of molecule: main group, hydrogen bonded, and transition metal systems. Expanding the OEP in the orbital basis leads to physically sensible exchange-correlation potentials; OEP generalized gradient approximation results provide some indication of the accuracy of the expansion. OEP uncoupled magnetic parameters from representative hybrid and Coulomb-attenuated functionals can be a dramatic improvement over conventional results; both categories yield similar accuracy. Additional flexibility is introduced by expanding the OEP in an extensive even-tempered basis set, but this leads to the well-known problem of unphysical, oscillatory potentials. Smooth potentials are recovered through the use of a smoothing norm, but deficiencies in the procedure are highlighted for transition metal complexes. The study reiterates the importance of the OEP procedure in magnetic response calculations using orbital-dependent functionals, together with the need for careful attention to ensure physically sensible potentials. It also illustrates the utility of Coulomb-attenuated functionals for computing short-range molecular properties.