Scaling Up DNA Origami Lattice Assembly

The surface-assisted hierarchical assembly of DNA origami nanostructures is a promising route to fabricate regular nanoscale lattices. In this work, the scalability of this approach is explored and the formation of a homogeneous polycrystalline DNA origami lattice at the mica-electrolyte interface over a total surface area of 18.75 cm² is demonstrated. The topological analysis of more than 50 individual AFM images recorded at random locations over the sample surface showed only minuscule and random variations in the quality and order of the assembled lattice. The analysis of more than 450 fluorescence microscopy images of a quantum dot-decorated DNA origami lattice further revealed a very homogeneous surface coverage over cm² areas with only minor boundary effects at the substrate edges. At total DNA costs of € 0.12 per cm², this large-scale nanopatterning technique holds great promise for the fabrication of functional surfaces.     

First-principles theory of the EPR g tensor in solids: defects in quartz

A theory for the reliable prediction of the EPR g tensor for paramagnetic defects in solids is presented. It is based on density functional theory and on the gauge including projector augmented wave approach to the calculation of all-electron magnetic response. The method is validated by comparison with existing quantum chemical and experimental data for a selection of diatomic radicals. We then perform the first prediction of EPR g tensors in the solid state and find the results to be in excellent agreement with experiment for the E(1)(prime) and substitutional phosphorus defect centers in quartz.     

First-principles calculation of 17O and 25Mg NMR shieldings in MgO at finite temperature: rovibrational effect in solids

The temperature dependence of (17)O and (25)Mg NMR chemical shifts in solid MgO have been calculated using a first-principles approach. Density functional theory, pseudopotentials, a plane-wave basis set, and periodic boundary conditions were used both to describe the motion of the nuclei and to compute the NMR chemical shifts. The chemical shifts were obtained using the gauge-including projector augmented wave method. In a crystalline solid, the temperature dependence is due to both (i) the variation of the averaged equilibrium structure and (ii) the fluctuation of the atoms around this structure. In MgO, the equilibrium structure at each temperature is uniquely defined by the cubic lattice parameters, which we take from experiment. We evaluate the effect of the fluctuations within a quasiharmonic approximation. In particular, the dynamical matrix, defining the harmonic Hamiltonian, has been computed for each equilibrium volume. This harmonic Hamiltonian was used to generate nuclear configurations that obey quantum statistical mechanics. The chemical shifts were averaged over these nuclear configurations. The results reproduce the previously published experimental NMR data measured on MgO between room temperature and 1000 degrees C. It is shown that the chemical shift behavior with temperature cannot be explained by thermal expansion alone. Vibrational corrections due to the fluctuations of atoms around their equilibrium position are crucial to reproduce the experimental results.     

Electronic-enthalpy functional for finite systems under pressure

We introduce the notion of electronic enthalpy for first-principles structural and dynamical calculations of finite systems under pressure. An external pressure field is allowed to act directly on the electronic structure of the system studied via the ground-state minimization of the functional E+PV(q), where V(q) is the quantum volume enclosed by a charge isosurface. The Hellmann-Feynman theorem applies, and assures that the ionic equations of motion follow an isoenthalpic dynamics. No pressurizing medium is explicitly required, while coatings of environmental ions or ligands can be introduced if chemically relevant. We apply this novel approach to the study of group-IV nanoparticles during a shock wave, highlighting the significant differences in the plastic or elastic response of the diamond cage under load, and their potential use as novel nanostructured impact-absorbing materials.     

Nonlocal pseudopotentials and magnetic fields

We show how to describe the coupling of electrons to nonuniform magnetic fields in the framework of the widely used norm-conserving pseudopotential approximation for electronic structure calculations. Our derivation applies to magnetic fields that are smooth on the scale of the core region. The method is validated by application to the calculation of the magnetic susceptibility of molecules within density functional theory (DFT) in the local density approximation. Our results are compared with high-quality all-electron DFT results obtained using Gaussian basis sets and another recently proposed pseudopotential formalism.     

Experimental pressure dependence of positive corona discharge in N $_\mathsf{2}$

This paper presents the experimental pressure dependence, in the range 1.01 x 10⁵-1.6 x 10⁵ Pa, of the I-V characteristic of a N₂ positive corona discharge. The pressure raise is related to the gas flow increase into the chamber where the corona is ignited. Experimental measurements confirm Townsends I-V characteristic. For a fixed potential difference between the electrodes, corona currents decrease as the gas flow increases (pressure increase): this has been ascribed to a lower ionization rate close to the stressed electrode and a lower charge mobility in the drift region. Both these processes result in a lower current generated by the discharge.Received: 5 February 2003, Published online: 30 July 2003PACS: 52.80.Hc Glow; corona