Quantum mechanical embedding theory based on a unique embedding potential

We remove the nonuniqueness of the embedding potential that exists in most previous quantum mechanical embedding schemes by letting the environment and embedded region share a common embedding (interaction) potential. To efficiently solve for the embedding potential, an optimized effective potential method is derived. This embedding potential, which eschews use of approximate kinetic energy density functionals, is then used to describe the environment while a correlated wavefunction (CW) treatment of the embedded region is employed. We first demonstrate the accuracy of this new embedded CW (ECW) method by calculating the van der Waals binding energy curve between a hydrogen molecule and a hydrogen chain. We then examine the prototypical adsorption of CO on a metal surface, here the Cu(111) surface. In addition to obtaining proper site ordering (top site most stable) and binding energies within this theory, the ECW exhibits dramatic changes in the p-character of the CO 4σ and 5σ orbitals upon adsorption that agree very well with x-ray emission spectra, providing further validation of the theory. Finally, we generalize our embedding theory to spin-polarized quantum systems and discuss the connection between our theory and partition density functional theory.     

A new tool to assess ceramide bioactivity: 6-bromo-7-hydroxycoumarinyl-caged ceramide

The bioactivity of natural, long-chain ceramides has until now been studied after its delivery to cells in organic solvent mixtures containing dodecane. We have synthesized ceramides conjugated to a (6-bromo-7-hydroxycoumarin-4-yl)methyl group. The photocaged ceramide is efficiently released with 350 nm light in aqueous solution at neutral pH, thus providing a promising new tool to study ceramide's properties.     

Crystal structures, EPR and magnetic properties of 2-ClC6H4CNSSN˙ and 2,5-Cl2C6H3CNSSN˙

The β-sheet structure associated with chlorinated aromatics (d(Cl···Cl)≈ 4.0 ?) has been implemented to drive formation of π-stacked structures of dithiadiazolyl radicals. Both title compounds exhibit an increase in paramagnetism above 150 K but solid-state EPR studies indicate that the origin of the paramagnetism in these two systems is different.     

Testing variations of the GW approximation on strongly correlated transition metal oxides: hematite (α-Fe2O3) as a benchmark

Quantitative characterization of low-lying excited electronic states in materials is critical for the development of solar energy conversion materials. The many-body Green's function method known as the GW approximation (GWA) directly probes states corresponding to photoemission and inverse photoemission experiments, thereby determining the associated band structure. Several versions of the GW approximation with different levels of self-consistency exist in the field. While the GWA based on density functional theory (DFT) works well for conventional semiconductors, less is known about its reliability for strongly correlated semiconducting materials. Here we present a systematic study of the GWA using hematite (α-Fe(2)O(3)) as the benchmark material. We analyze its performance in terms of the calculated photoemission/inverse photoemission band gaps, densities of states, and dielectric functions. Overall, a non-self-consistent G(0)W(0) using input from DFT+U theory produces physical observables in best agreement with experiments.     

A re-examination of the induction (crystal field) energy contribution to the relative stabilities of the f.c.c. and h.c.p. rare-gas crystal structures

A new calculation of the induction (crystal field) energy of the f.c.c. and h.c.p. structures of the rare-gas crystals of neon and argon gives an energy in favour of f.c.c. which is more than sufficient to counter the summed pair-potential which favours h.c.p. Predicted values of (E _f.c.c. - E _h.c.p.)/E _f.c.c. for neon and argon are 0·9 × 10^-3 and 1·3 × 10^-3 respectively. These values are similar to those that have been obtained for a modified dispersion energy and it is concluded that they should be added to these dispersion energies. Calculations on solid helium show a negligible difference in the induction energy for the two close-packed structures.     

A lower bound for the number of Reidemeister moves of type III

We study the number of Reidemeister type III moves using Fox n-colorings of knot diagrams.     

80–360 GHz very wide band millimeter wave network analyzer

An extension to a 20 GHz HP8510C Network Analyzer has been built for wideband measurements between 80 and 360 GHz. Improvements relative to the first version [1], [2] include new harmonic mixers, and an active doubler. Dynamic ranges up to 60 dB in transmission and 50 dB in reflection are obtained up to 280 GHz, with more than 50 GHz instantaneous bandwidth using waveguide calibration. Detection with a 30 dB dynamic range is obtained at 320 – 360 GHz. Time domain measurements give spatial resolution down to 2 mm.     

Nuclear moments of the neutron-deficient thallium isotopes

The nuclear moments of the neutron-deficient^187,188Tl isotopes were determined by measuring the hyperfine structure splittings of the λ=535 nm line in neutral thallium. An optical efficiency of 2×10⁻⁴ photons per radioactive ion was achieved using collinear fast beam laser spectroscopy with a large solid angle fiber optical array detector. Most of the moments can be interpreted fairly well in the single particle model.