Pseudopotential-fragment spectroscopy for organic molecules and carbon allotropes

Following on from a previous work (Punter et al., IJQC 2019, 119, 23), pseudopotential sets are developed and tested for a variety of sp² and sp³ carbon fragments. These fragments contain only one or two explicit protons and electrons, and make use of non-atom-centered potentials. They are tested with density functional theory calculations in a selection of chemical environments in which several physical characteristics, including orbital and first ionization energies, are found to be well reproduced. They are then employed in the reproduction of molecular absorption spectra for large organic molecules and carbon allotropes, and are found to recreate both absorption and electronic circular dichroism spectra to a high accuracy. They are also found significantly to increase the computational efficiency of time dependent density functional theory (TDDFT) calculations in which they are used.     

Mimics of peptide turn backbone and side-chain geometry by a general approach for modifying azabicyclo[5.3.0]alkanone amino acids

Peptide mimics with constrained backbone and side-chain geometry are important tools for studying structure activity relationships of biologically active candidates. A general method for creating β-turn mimics possessing side-chain diversity has been developed featuring diastereoselective S(N)1 displacements of an iodide precursor. In particular, 6-iodo-pyrroloazepin-2-one amino ester 10 has served as a common precursor in reactions with a variety of alcohol, phenol, nitrate, and azide nucleophiles to provide an array of constrained peptide mimics.     

螺旋波激发甲烷等离子体光谱诊断

利用螺旋波激发等离子体化学气相沉积(LPP-CVD)技术,以甲烷和氦气为反应气体产生等离子体.通过采集到甲烷的可见光到紫外发射光谱,对甲烷等离子体进行原位诊断,发现存在CH、Ha及Hβ等碎片粒子的光辐射,同时,分析了不同入射功率、气压下CH粒子以及Hβ、Hγ的相对强度变化情况.结果表明:CH粒子的相对强度随着射频功率是先增大而后减小,随工作气压的增大而逐渐减小;随气压及功率的增加,Hβ、Hγ相对强度变化的总体趋势都是先增加而后减小的.     

Setting targets for surrogate-based optimization

In the context of surrogate-based optimization (SBO), most designers have still very little guidance on when to stop and how to use infill measures with target requirements (e.g., one-stage approach for goal seeking and optimization); the reason: optimum estimates independent of the surrogate and optimization strategy are seldom available. Hence, optimization cycles are typically stopped when resources run out (e.g., number of objective function evaluations/time) or convergence is perceived, and targets are empirically set which may affect the effectiveness and efficiency of the SBO approach. This work presents an approach for estimating the minimum (target) of the objective function using concepts from extreme order statistics which relies only on the training data (sample) outputs. It is assumed that the sample inputs are randomly distributed so the outputs can be considered a random variable, whose density function is bounded (a, b), with the minimum (a) as its lower bound. Specifically, an estimate of the minimum (a) is obtained by: (i) computing the bounds (using training data and the moment matching method) of a selected set of analytical density functions (catalog), and (ii) identifying the density function in the catalog with the best match to the sample outputs distribution and corresponding minimum estimate (a). The proposed approach makes no assumption about the nature of the objective functions, and can be used with any surrogate, and optimization strategy even with high dimensional problems. The effectiveness of the proposed approach was evaluated using a compact catalog of Generalized Beta density functions and well-known analytical optimization test functions, i.e., F2, Hartmann 6D, and Griewangk 10D and in the optimization of a field scale alkali-surfactant-polymer enhanced oil recovery process. The results revealed that: (a) the density function (from a catalog) with the best match to a function outputs distribution, was the same for both large and reduced samples, (b) the true optimum value was always within a 95% confidence interval of the estimated minimum distribution, and (c) the estimated minimum represents a significant improvement over the present best solution and an excellent approximation of the true optimum value.     

Atomic pseudopotentials for reproducing π-orbital electron behavior in sp2 carbon atoms

A pseudopotential system for an sp² carbon atom is built and tested as a building block for various pseudohydrocarbon polyenes and polycyclic aromatic hydrocarbons. This pseudosystem has a central charge of Z = 1; it contains only one electron. It is employed in ab-initio calculations in which several physical characteristics including the orbital energies and first ionization energy, as well as first excitation energy and UV spectra, are found to be well-reproduced by the pseudosystem. Remarkably, not only are the π excitation energies in good agreement with the reference calculations, but also transition densities and intensities, confirming that the virtual space obtained with the pseudopotentials is of excellent quality. Finally, this approach is capable of reproducing the π electron systems of small or large, planar or nonplanar hydrocarbons at low computational cost.     

Mathematical modeling and simulation of the reaction environment in electrochemical reactors

An electrochemical reactor, enabling controlled flow and capable of including a varied range of forms of electrodes, is important in the studies of electrochemical processes, such as energy production and storage, electrosynthesis of chemicals, electrowinning of metals, purification of water, wastewater treatment, remediation of soils, and so on, before the process development and scale-up. Here, we reviewed recent advances in modeling and simulation of the reaction environment in many electrochemical reactors used in multiple applications. The importance of computational fluid dynamics simulations to study existing reactors and to design novel reactor geometries and some components of existing cells is discussed. Aspects include the effect of electrolyte velocity on the flow dispersion, mass transport rates, and current distribution.     

Oxidation of benzoins to benzils in the presence of porphyrin sensitizers by air and sunlight or visible light

In this work, two new aerobic routes are introduced for the oxidation of a variety of benzoins to benzils by using molecular oxygen in the presence of porphyrins as sensitizers, using white light or sunlight in acetonitrile under mild conditions. The methods have a wide range of applications, do not involve cumbersome work-up, exhibit chemoselectivity and proceed under mild reaction conditions. The resulting products are obtained in good yields in a reasonable time.     

A new sample holder for excitation of transverse sound waves

A simple non-resonant sample holder with inclined electrodes is described by means of which transverse sound waves in the GHz range are easily generated by an evaporated piezoelectric layer. Because of its small size it is especially well suited for cryostat applications.     

60Co retention by Mexican montmorillonites

Radioactive elements may be retained by clays. The ability of natural Mexican clays to retain radioactive Co from aqueous solutions, is discussed. Experiments were performed with solutions containing labeled cobalt. The effect of contact time on Co²⁺ retention was studied. It was found that the Co²⁺ uptake value in dehydrated montmorillonites is between 0.30 and 0.70 meq g^–1 of clay. A sorption sequence was obtained for the various clays. The samples were characterized, before and after cobalt exchange, by X-ray diffraction.