JACOB: An enterprise framework for computational chemistry

Here, we present just a collection of beans (JACOB): an integrated batch‐based framework designed for the rapid development of computational chemistry applications. The framework expedites developer productivity by handling the generic infrastructure tier, and can be easily extended by user‐specific scientific code. Paradigms from enterprise software engineering were rigorously applied to create a scalable, testable, secure, and robust framework. A centralized web application is used to configure and control the operation of the framework. The application‐programming interface provides a set of generic tools for processing large‐scale noninteractive jobs (e.g., systematic studies), or for coordinating systems integration (e.g., complex workflows). The code for the JACOB framework is open sourced and is available at: www.wallerlab.org/jacob . © 2013 Wiley Periodicals, Inc.     

Single‐wall carbon nanotube interactions with copper‐oxamato building block of molecule‐based magnets probed by resonance Raman spectroscopy

The electronic interactions between the [Cu(opba)]²⁻ anions (where opba is orthophenylenebis (oxamato)) and single‐wall carbon nanotubes (SWCNTs) were investigated by resonance Raman spectroscopy. The opba can form molecular magnets, and the interactions of opba with SWCNTs can produce materials with very different magnetic/electronic properties. It is observed that the electronic interaction shows a dependence on the SWCNT diameter independent of whether they are metallic or semiconducting, although the interaction is stronger for metallic tubes. The interaction also is dependent on the amount of complex that is probably adsorbed on the carbon surface of the SWCNTs. Some charge transfer can be also occurring between the metallic complex and the SWCNTs. Copyright © 2012 John Wiley & Sons, Ltd.     

PRESSURE-VELOCITY EQUILIBRIUM HYDRODYNAMIC MODELS

This article describes mathematical models for phase separated mixtures of materials that are in pressure and velocity equilibrium but not necessarily temperature equilibrium. General conditions for constitutive models for such mixtures that exhibit a single mixture sound speed are discussed and specific examples are described.     

Transport properties of copper-doped carbon aerogels

The magnetic susceptibility, conductivity, magnetoresistance (MR) and Hall effect of copper-doped carbon aerogels are measured and compared with corresponding results from the original carbon aerogels. The experimental results indicate that the temperature-dependent magnetic susceptibility of the copper-doped and of the original carbon aerogels is well fit by a Curie function at low temperatures. The copper-doped carbon aerogels show a higher susceptibility and spin concentration than the original carbon aerogel. After doping by copper, the materials exhibit a more linear current-voltage curve than the original carbon aerogel under the same measurement conditions. The electrical resistance of the copper-doped carbon aerogels is strikingly lower than that of the original carbon aerogels, and decreases with increasing copper content in the samples. The temperature-dependent resistivity ρ(T) of all of the copper-doped and original carbon aerogels can be fitted by an exp(T^−1/2) dependence for T<100 K. The copper-doped and pristine carbon aerogels follow a quadratic MR behavior Δρ/ρ=AB² in the magnetic field range B investigated (up to 5 T), except at very low temperatures (T<4 K).     

Effect of Pr-Ca substitution on the transport and magnetic behavior of LaMnO3 perovskite

The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO₃ perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La_1−2x Pr _x Ca _x )MnO₃ (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T _c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for understanding the structural, transport and magnetic properties are discussed in detail.     

Temperature dependence of C-axis electrical resistivity and thermopower of graphite intercalation compounds

Results on the temperature variation from 2 ? T ? 300 K of the c-axis electrical resistivity and thermopower of a donor stage-5 potassium and an acceptor stage-2 FeCl₃ graphite intercalation compounds are reported. Comparing the data with those of the literature reveals for both compounds a different qualitative behavior for low and high stages.     

Optical absorption of EuTe in high magnetic fields

For the first time, the optical absorption edge of the magnetic semiconductor europium telluride has been studied at low temperature (1.7 K) as a function of magnetic field in the high field range 0 ≤ H ≤ 9.5 Tesla, and related to the magnetic phase diagram of this material. The exponential absorption edge has been parameterized using a magnetic field dependent extension of Urbach's rule, and the observations are found to be consistent with a simple dependence of the gap parameter on polarization and magnetic field.     

Chemisorbed phases of H2O on TiO2 and SrTiO3

Ultraviolet photoemission spectroscopy in ultrahigh vacuum has been used to study the interaction of H₂O with argon-ion-bombarded and annealed TiO₂(110) and SrTiO₃ (100) surfaces. At low exposure, evidence is found for the presence of the OH free radical on both bombarded and annealed TiO₂. At high exposure, a spectrum of slightly perturbed adsorbed H₂O is observed, with the a₁ molecular orbital shifted 0.5–1 eV toward tighter binding. This suggests that H₂O binds to the surface of TiO₂ via its a₁, in-plane O lone-pair orbital. No evidence is found for OH on the surface of SrTiO₃. The spectrum of H₂O adsorbed on bombarded SrTiO₃ shows both the a₁ and b₂ molecular orbitals shifted 0.4 toward tighter binding, indicating a more complicated bonding to the surface. For SrTiO₃ that has been bombarded and then annealed, the spectrum of adsorbed H₂O shows no significant bonding effects.     

Low temperature thermal conductivity of graphite-FeCl3 intercalation compounds

The low-temperature variation of the in-plane thermal conductivity of graphite- FeCl₃ intercalation compounds is reported. Around room temperature, though holes are participating, there is an important lattice contribution, but much smaller than in pristine graphite. The electronic contribution dominates in the liquid helium range. These preliminary results suggest lattice thermal conductivity measurements as a new tool to investigate defects introduced by intercalation.     

Low frequency longitudinal lattice modes in graphite intercalation compounds

Results of inelastic neutron scattering experiments on a stage 2 graphite-FeCl₃ intercalation compound are reported. A one-dimensional Born-von Kármán model is formulated and applied to interpret the data. The application of this model to other recently reported neutron data for donor compounds suggests systematic trends in the magnitudes of the interactions, dependent on the intercalate sandwich thickness.