A DFT study of carbon nanobuds

In the framework of the density functional theory (DFT) calculations, we present a first time investigation of the properties of four kinds of configurations of carbon nanobuds (CNBs) in which a perfect or defective C60 molecule attaches covalently on the surface of an armchair single-walled carbon nanotube (SWCNT). Chemical shielding (CS) parameters were calculated for the optimized structures. Our results indicate that carbon nanobuds have different values of formation energy, band gap energy, dipole moment, charge transfer and chemical-shielding isotropy (CSI), which result from the many covalent combinations of the fullerenes with the carbon nanotubes. These calculations were carried out using the Gaussian 09 software package.     

Spurious currents in finite element based level set methods for two‐phase flow

A study of spurious currents in continuous finite element based simulations of the incompressible Navier–Stokes equations for two‐phase flows is presented on the basis of computations on a circular drop in equilibrium. The conservative and the standard level set methods are used. It is shown that a sharp surface tension force, expressed as a line integral along the interface, can give rise to large spurious currents and oscillations in the pressure that do not decrease with mesh refinement. If instead a regularized surface tension representation is used, exact force balance at the interface is possible, both for a fully coupled discretization approach and for a fractional step projection method. However, the numerical curvature calculation introduces errors that cause spurious currents. Different ways to extend the curvature from the interface to the whole domain are discussed and investigated. The impact of using different finite element spaces and stabilization methods is also considered. Copyright © 2011 John Wiley & Sons, Ltd.     

Sustainable conversion of carbon dioxide to formic acid with Rh-decorated phosphorous-doped fullerenes: a theoretical study

Structural Chemistry - We performed density functional calculations to study conversion of carbon dioxide to formic acid through designed catalyst of Rh-decorated phosphorous-doped fullerenes. Two...     

A conservative level set method for contact line dynamics

A new model for simulating contact line dynamics is proposed. We apply the idea of driving contact-line movement by enforcing the equilibrium contact angle at the boundary, to the conservative level set method for incompressible two-phase flow [E. Olsson, G. Kreiss, A conservative level set method for two phase flow, J. Comput. Phys. 210 (2005) 225–246]. A modified reinitialization procedure provides a diffusive mechanism for contact-line movement, and results in a smooth transition of the interface near the contact line without explicit reconstruction of the interface. We are able to capture contact-line movement without loosing the conservation. Numerical simulations of capillary dominated flows in two space dimensions demonstrate that the model is able to capture contact line dynamics qualitatively correct.     

A new approach to determine radiative recombination lifetime in quantum well solar cells

In this paper, the authors present and extend on an existing model, which has been developed to determine the radiative recombination lifetimes in quantum well solar cells. Given the fact that recombination reduces cell performance, the main future use of this new model is to aid in optimisation of cell designs and increase cell efficiency. In this work the authors introduce a coefficient defined as the delta factor which is based on material parameters into the existing model. The introduction of this factor into the existing model has shown an improvement in radiative recombination lifetime determination of approximately 11% when comparison is made with the previous model. This has lead to an overall average improvement in lifetime determination of approximately 9% when comparisons are made between the new model and experimental data. This is a significant improvement in lifetime determination, which will benefit cell designers.     

Understanding the kinetics and mechanism of thermal cheletropic elimination of N<Subscript>2</Subscript> from (2,5-dihydro-1<Emphasis Type="Italic">H</Emphasis>-pyrrol-1-ium-1-ylidene) amide using RRKM and ELF theories

The cheletropic elimination process of N₂ from (2,5-dihydro-1H-pyrrol-1-ium-1-ylidene) amide (C₄H₆N₂) has been studied computationally using density functional theory, along with the M06-2X/aug-cc-pVTZ level of theory. The calculated energy profile has been supplemented with calculations of kinetic rate constants using transition state theory (TST) and statistical Rice–Ramsperger–Kassel–Marcus (RRKM) theory. This elimination process takes place spontaneously with an activation energy around 33 kJ/mol. Pressure dependence of the rate constants revealed that the TST approximation breaks down and fall-off expression is necessary for the kinetic modeling. At temperatures ranging from 240 to 360 K and atmospheric pressure, the unimolecular rate constant is evaluated from RRKM theory as \(k_{{(240 - 360\,{\text{K}})}}^{{1.0{\text{atm}}}} = 1.0249 \times 10^{12} \times {\text{e}}^{{ - \frac{{33.11\;{\text{kJ}}/{\text{mol}}}}{RT}}} \,{\text{s}}^{ - 1}\). Bonding changes along the reaction coordinate have been studied using bonding evolution theory. Electron localization function topological analysis reveals that the cheletropic elimination is characterized topologically by four successive structural stability domains (SSDs). Breaking of C–N bonds (Rx = 0.1992 amu^1/2 Bohr) and the other selected points separating the SSDs along the reaction coordinate occur in the vicinity of the transition state.     

Identifying and mitigating residual vibrations in wave-based control of lumped,flexible systems

Meccanica - Wave-based control (WBC) is a technique for motion control of under-actuated flexible systems. It envisages actuator motion as launching a motion wave into the system, while...     

Mechanism and regioselectivity of the 1,3‐dipolar cycloaddition of thiocarbonyl S‐imide with cyclopent‐3‐ene‐1,2‐dione and methoxyethene: a density functional theory approach

A theoretical study on the regioselectivity of 1,3‐dipolar cycloaddition reaction between an uncommon dipole (thiocarbonyl S‐imide) with cyclopent‐3‐ene‐1,2‐dione (DPh1) and methoxyethene (DPh2) has been carried out by means of several theoretical approaches, namely, activation energy, Houk's rule based on the frontier molecular orbital theory and density functional theory (DFT) reactivity indices. The calculations were performed at the DFT‐B3LYP/6‐31G(d) level of theory using GAUSSIAN 09. The present analysis shows that the 1,3‐dipolar cycloaddition of thiocarbonyl S‐imide with DPh1 and DPh2 has normal‐electron demand and inverse‐electron demand character, respectively. Moreover, the results obtained from energetic point view are in agreement with electronic approaches, and the Houk's rule is capable to predict true regioselectivity. Copyright © 2012 John Wiley & Sons, Ltd.     

Theoretical study on the mono and multiply oxygenated Si60H60 fullerene

We have applied density functional theory (DFT) calculations to study the structures, stabilities, electronic and magnetic properties of mono and multiply oxygenated Si₆₀H₆₀ fullerenes (Si₆₀H_60–2nO_n, n = 1, 3, 6, 9, 10, 12, 18, 20, 21, 27 and 30). DFT results show that rearrangement between the closed [6,6] and [5,6] isomers of Si₆₀H₅₈O follows a two-step pathway involving an intermediate and two transition states. Preserving the C₃ symmetry in the cage structure, extra epoxidation of Si₆₀H₆₀ has been accomplished. Based on our results, formation energies per oxygen atom for the multiple additions of oxygen atoms on Si₆₀H₆₀ cage are positive (endothermic character), and increase with the increasing of the number of oxygen atoms. In general, the oxygenation of Si₆₀H₆₀ cage leads to an increase in the electrophilicity of the Si₆₀H_60–2nO_n oxides. The oxygenation of Si–Si bonds not only introduces a substantial broadening of the NMR pattern but also yield individual peaks, indicating different electrostatic environments of silicon nuclei in the Si₆₀H_60–2nO_n oxides.     

Simultaneous determination of carbazole-based explosives in environmental waters by dispersive liquid—liquid microextraction coupled to HPLC with UV-Vis detection

Dispersive liquid-liquid microextraction as a rapid, simple and efficient method coupled with high performance liquid chromatography-UV-Vis detection was used for sample preparation and subsequent determination of carbazole, tri nitro carbazole (TrNC) and tetra nitro carbazole in water samples. The influence of several important variables on the extraction efficiency has been evaluated. The methods works best with chloroform as an extractant and acetonitrile as the dispersive solvent. Under optimum conditions, the calibration curve is linear in the range from 0.007 to 1.75?μg?mL^?1 for TNC, 0.006 to 1.52?μg?mL^?1 for TrNC, and 0.008–2.10?μg?mL^?1 for carbazole. The limits of detection (LODs; at a signal-to-noise ratio of 3), range from 1.7 to 1.1?ng?mL^?1, for TNC, TrNC and carbazole. Also, the relative standard deviations (RSD, n?=?6) for the extraction of TNC (at 174?ng?mL^?1), TrNC (at 151?ng?mL^?1) and carbazole (at 84?ng?mL^?1) vary between 4.1 and 5.2%. The enrichment factors range from 179 to 186. The method was successfully applied to the determination of TNC, TrNC and carbazole in environmental samples.