With the advent of efficient electronic structure methods, effective continuum solvation methods have emerged as a way to, at least partially, include solvent effects into simulations without the need for expensive sampling over solvent degrees of freedom. The multipole moment expansion (MPE) model, while based on ideas initially put forward almost 100 years ago, has recently been updated for the needs of modern electronic structure calculations. Indeed, for an all-electron code relying on localized basis sets and-more importantly-a multipole moment expansion of the electrostatic potential, the MPE method presents a particularly cheap way of solving the macroscopic Poisson equation to determine the electrostatic response of a medium surrounding a solute. In addition to our implementation of the MPE model in the FHI-aims electronic structure theory code [ Blum , V. ; Comput. Phys. Commun. 2009 , 180 , 2175 - 2196 , DOI: 10.1016/j.cpc.2009.06.022 ], we describe novel algorithms for determining equidistributed points on the solvation cavity-defined as a charge density isosurface-and the determination of cavity surface and volume from just this collection of points and their local density gradients. We demonstrate the efficacy of our model on an analytically solvable test case, against high-accuracy finite-element calculations for a set of ≈140000 2D test cases, and finally against experimental solvation free energies of a number of neutral and singly charged molecular test sets [ Andreussi , O. ; J. Chem. Phys. 2012 , 136 , 064102 , DOI: 10.1063/1.3676407 ; Marenich , A. V. ; Minnesota Solvation Database , Version 2012; University of Minnesota : Minneapolis, MN, USA , 2012 . ]. In all test cases we find that our MPE approach compares very well with given references at computational overheads < 20% and sometimes much smaller compared to a plain self-consistency cycle.

The fabrication of highly active and robust hexagonal ruthenium oxide nanosheets for the electrocatalytic oxygen evolution reaction (OER) in an acidic environment is reported. The ruthenate nanosheets exhibit the best OER activity of all solution‐processed acid medium electrocatalysts reported to date, reaching 10 mA cm−2 at an overpotential of only ≈255 mV. The nanosheets also demonstrate robustness under harsh oxidizing conditions. Theoretical calculations give insights into the OER mechanism and reveal that the edges are the origin of the high OER activity of the nanosheets. Moreover, the post OER analyses indicate, apart from coarsening, no observable change in the morphology of the nanosheets or oxidation states of ruthenium during the electrocatalytic process. Therefore, the present investigation suggests that ruthenate nanosheets are a promising acid medium OER catalyst with application potential in proton exchange membrane electrolyzers and beyond.

Vicinal scalar J-coupling constants in polypeptides are analyzed using density functional theory (DFT) in combination with molecular dynamics (MD) computer simulations. The couplings studied are the six 3 J-coupling constants that involve the φ backbone torsion angle, 3 J(, and 3 J(C′-C′), and two 3 J-coupling constants, 3 J(H R -N) and 3 J(N-N), that involve the ψ backbone torsion angle. The dependence of these couplings on their main torsion angle as well as other degrees of freedom are investigated by computations performed on two different versions of the alanine dipeptide, Ala-Ala-NH 2 and Ace-Ala-NMe, with sets of coordinates obtained by different structure optimization schemes and from snapshots extracted from a MD trajectory of ubiquitin. In this way, assumptions that underlie the widely used Karplus relationships can be independently tested. Static Karplus curves, which are fitted to the computed couplings as a function of the φ-torsion angle, are generally in good agreement with empirical Karplus curves reported for several proteins if substantial motional averaging effects are taken into account. For ubiquitin, the average φ-angle fluctuation amplitudes are (24°, which is somewhat larger than what has been found from NMR relaxation measurements and MD simulations, presumably because these latter techniques predominantly reflect motions on the ns and sub-ns time-scale range. Systematic differences in the backbone φ angles between the solution-state and the crystalline structure are found to play a minor role. The two J couplings involving the ψ angle are sensitive not only to their main torsion angle, but also to other degrees of freedom, which may complicate their interpretation. The emergence of DFT as a quantitative tool for the interpretation of scalar J-coupling constants enhances the power of J-coupling analysis as a unique probe of structural dynamics of biomolecules.

We optically probe and electrically control a single artificial molecule containing a well defined number of electrons. Charge and spin dependent interdot quantum couplings are probed optically by adding a single electron-hole pair and detecting the emission from negatively charged exciton states. Coulomb- and Pauli-blockade effects are directly observed, and tunnel coupling and electrostatic charging energies are independently measured. The interdot quantum coupling is shown to be mediated by electron tunneling. Our results are in excellent accord with calculations that provide a complete picture of negative excitons and few-electron states in quantum dot molecules.

The interpretation of nuclear spin relaxation data of biomolecules often requires the accurate knowledge of chemical shielding anisotropy (CSA) tensors, which significantly depend on the environment and on intramolecular dynamics. CSA tensors are studied in this work by density functional theory and by molecular dynamics simulations. It is demonstrated that density functional theory yields CSA tensors for 15 N nuclei in the side chain of crystalline asparagine and in the peptide bond of crystalline alanine-alanine dipeptide with an accuracy comparable to that of solid-state NMR. In these calculations, the molecular fragment containing the nucleus of interest is treated with an IGLO-II and IGLO-III basis set while neighboring fragments exhibiting close contacts are represented by a DZVP set. In addition, electrostatic effects are taken into account by explicit partial point charges. The dynamical averaging of CSA tensors is investigated by applying density functional theory to snapshots of a molecular dynamics trajectory of the protein ubiquitin. The fluctuation properties of the 15 N CSA tensors of two glutamine side chains are assessed. Computed auto-and cross-correlated relaxation parameters using these CSA tensors are found to be in good agreement with the experiment. Local charges and close contacts can have a significant effect on 15 N CSA tensors and have to be taken into account when transferring CSA parameters from model compounds to proteins.

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An ensemble of exciton Hamiltonians for the amide-I band of the folded and unfolded states of a helical beta-heptapeptide is generated using a molecular dynamics (MD) simulation. The correlated fluctuations of its parameters and their signatures in two-dimensional (2D) vibrational echo spectroscopy are computed. This technique uses infrared pulse sequences to provide ultrafast snapshots of molecular structural fluctuations, in analogy with multidimensional NMR. The present study demonstrates that, by combining a method of calculating the vibrational Hamiltonian from MD snapshots and the nonlinear exciton equations (NEE), it may be possible to simulate realistic multidimensional IR spectra of chemically and biologically interesting systems.

A unified description of resonant multiple-pulse experiments in coupled spin-12 systems in NMR spectroscopy and two-level systems in optical spectroscopy is presented. The connection between the NMR product operator formalism and the Liouville space pathways in optical spectroscopy is established. We show how the information obtained in various strong field two and three pulse NMR experiments can be extracted by combining heterodyne detected phase-controlled weak field signals generated at different directions. These results allow the design of sequences of weak optical pulses that accomplish the same goals as strong field multidimensional NMR spectroscopy.