Small and efficient basis sets for the evaluation of accurate interaction-induced linear and non-linear electric properties in model hydrogen-bonded complexes

Interaction-induced electric dipole moment, polarisability and first hyperpolarisability are investigated in model hydrogen-bonded clusters built of hydrogen fluoride molecules organised in three linear chains parallel to each other. The properties are evaluated within the finite field approach, using the second order Møller–Plesset method, and the LPol-m (m = ds, dl) and the optical rotation prediction (ORP) basis sets. These bases and correlation method are selected after a systematic basis set and correlation method convergence study carried out on the smallest of the complexes and taking properties obtained with Dunning's bases and the coupled cluster singles and doubles (CCSD) and the CCSD including connected triple corrections (CCSD(T)) methods as reference. Results are analysed in terms of many-body and cooperative effects.     

Theoretical study of the SrLi+ molecular ion: structural,electronic and dipolar properties

ABSTRACT

The structural and electronic properties of (SrLi)⁺ molecular ion have been determined by the use of ab initio approaches. Potential energy curves (PECs) with their spectroscopic constants (R_e, D_e, ω_e, T_e, B_e and ω_eχ_e) have been calculated. Also, the vibrational properties and the electric dipole moments, either permanent (PDM) or transition (TDM) ones, have been investigated and analysed. Large Gaussian basis sets, the full valence configuration interaction (FCI) and the formalism of non-empirical pseudo-potential including the two approaches, effective core potential (ECP) and core polarisation potential (CPP), are analysed. Therefore, (SrLi)⁺ is considered as a two effective electrons system. Numerous excited states of symmetries ^1,3Σ⁺, ^1,3Π and ^1,3Δ dissociating below the ionic limit Sr²⁺Li^? have been investigated. This study shows interesting behaviours around the avoided crossing related to charge transfer involving important processes in physics and astrophysics such as dynamics, pre-dissociation and inelastic transitions.     

Geometries,spectra and photoelectric properties of trifluorenylamine-based photoactive layer

The ground-state geometries, electronic structures, spectra and photoelectric properties of two dyes (JA1 and JA2) used for dye-sensitised solar cells (DSSCs) have been investigated with density functional theory (DFT) and time-dependent density functional theory (TDDFT). For simulation of the realistic environment, we calculated the energy levels of molecular orbitals and absorption spectra in solvent, and the different electric fields have been considered. For interpreting the difference of photoelectric properties, we assessed the energy levels and energy gaps of frontier molecular orbitals, electron density, absorption, the total static first hyperpolarisability and driving force of electron injection. The relationship between structure and performance should be established. Furthermore, 24 dyes were designed on the basis of JA1 and JA2 to improve optical response and electron injection. The results of molecular modelling would provide the optional approach for improving performance of photoelectric materials.     

ELECTRIC FIELD-INDUCED DIRECTOR ORIENTATION OF SMECTIC-A DOMAINS IN AN ISOTROPIC PHASE

Abstract

Electric field-induced director orientation of smeetic-A phase in an isotropic phase has been studied with a polarizing microscope using the binary mixture of octyloxycyanobiphenyl and dodecyl alcohol. Electric field is applied to the samples in which spherical smectic-A domains with and without defects in an isotropic phase are observed. Field-induced orientation of smectic-A director is observed for spherical smectic-A domains with defects but not observed for those without defects below electric field strength of 1.0 V/μm, indicating that the presence of defects facilitates the director orientation. The threshold field for the smectic-A director orientation varies from smectic-A domain to domain, suggesting that the threshold field is dependent on the structure of defects.     

Vacuum pair-production in a classical electric field and an electromagnetic wave

Using semiclassical WKB-methods, we calculate the rate of electron–positron pair-production from the vacuum in the presence of two external fields, a strong (space- or time-dependent) classical field and a monochromatic electromagnetic wave. We discuss the possible medium effects on the rate in the presence of thermal electrons, bosons, and neutral plasma of electrons and protons at a given temperature and chemical potential. Using our rate formula, we calculate the rate enhancement due to a laser beam, and discuss the possibility that a significant enhancement may appear in a plasma of electrons and protons with self-focusing properties.     

Dielectric Dispersion Study of Poly(vinyl Pyrrolidone)–Polar Solvent Solutions in the Frequency Range 20 Hz–1 MHz

Influence of polar solvents environment and polymer concentrations on the electrical properties (complex dielectric constant, ac electrical conductivity, complex electric modulus and complex impedance) of the solutions of poly(vinyl pyrrolidone) (PVP) in polar solvents, namely water, ethyl alcohol, ethylene glycol, diethylene glycol, poly(ethylene glycol), glycerol, dimethyl sulfoxide and dimethyl formamide, have been investigated in the frequency range 20 Hz–1 MHz at 25°C. Comparative analysis of the dielectric dispersion curves confirms that the solvent molecular size and number of its hydroxyl groups, and the solutions viscosity, are the major factors which governs the PVP chain segmental motion. The ionic conduction and electrode polarization phenomena has a dominant influence on the large increase of complex dielectric constant values of the solutions of PVP‐polar solvent in the lower frequency region. The values of relaxation times corresponding to these phenomena are also reported.     

有机高分子链内的场致激子解离

基于SSH(Su-Schrieffer-Heeger)模型,采用静态及动力学自洽算法模拟了有机高分子链内激子在光激发及外电场作用下的形成与解离过程。结果表明,受光激发后,有机高分子链内激子的生成与解离密切依赖于施加外电场的时机,当外电场与光激发同时发生时,激子能否生成完全取决于电场强度的大小;而当外电场在光激发后的一段时间(通常为皮秒量级)之后被引入,则在有机高分子链内能够形成稳定的激子,且该激子只有在强外电场(超过1MV/cm)的作用下,才会发生解离,临界场强量级与实验结果相符合。     

基于电场数值加权的跨介质元胞共形新技术

针对时域有限差分法处理跨介质元胞现有共形技术中存在误差大、平行方向未被包含等问题, 提出一种利用电场数值加权法来进行跨介质元胞共形计算的新算法. 该算法不再对介电常数ε做加权平均处理, 而是根据中值定理对时域有限差分法真正的求解分量电场强度进行权值选择, 并将权值乘入积分路径中. 该方法同时考虑了跨介质安培环路元胞与跨介质法拉第环路元胞对结果带来的不连续影响, 而且对介质界面与元胞中场分量的各种位置关系均能应用, 通用性强、精度高且易于实现. 利用介质填充圆波导作为数值模型来进行理论数值计算和仿真验证, 比较不同共形方法的二维TE模式的特征根与理论值的偏差以及由共形技术所带来的各向相异性. 数值结果表明, 本文所提出算法求得的特征根最接近理论值, 而且造成的各向相异性更小, 从而验证了该算法在处理跨介质元胞时的有效性. 关键词： 时域有限差分 电场数值加权法 二维TE模式 跨介质元胞     

Effect of multiple engine placement on aeroelastic trim and stability of flying wing aircraft

Effects of multiple engine placement on flutter characteristics of a backswept flying wing resembling the HORTEN IV are investigated using the code NATASHA (Nonlinear Aeroelastic Trim And Stability of HALE Aircraft). Four identical engines with defined mass, inertia, and angular momentum are placed in different locations along the span with different offsets from the elastic axis while fixing the location of the aircraft c.g. The aircraft experiences body freedom flutter along with non-oscillatory instabilities that originate from flight dynamics. Multiple engine placement increases flutter speed particularly when the engines are placed in the outboard portion of the wing (60–70% span), forward of the elastic axis, while the lift to drag ratio is affected negligibly. The behavior of the sub- and supercritical eigenvalues is studied for two cases of engine placement. NATASHA captures a hump body-freedom flutter with low frequency for the clean wing case, which disappears as the engines are placed on the wings. In neither case is there any apparent coalescence between the unstable modes. NATASHA captures other non-oscillatory unstable roots with very small amplitude, apparently originating with flight dynamics. For the clean-wing case, in the absence of aerodynamic and gravitational forces, the regions of minimum kinetic energy density for the first and third bending modes are located around 60% span. For the second mode, this kinetic energy density has local minima around the 20% and 80% span. The regions of minimum kinetic energy of these modes are in agreement with calculations that show a noticeable increase in flutter speed if engines are placed forward of the elastic axis at these regions.     

Water structures inside and outside single-walled carbon nanotubes under perpendicular electric field

The structures of water inside and outside(6,6),(8,8), and(10,10) singlewalled carbon nanotubes(SWCNTs) under an electric field perpendicular to the tube axis are investigated by molecular dynamics simulations. The results show that dipole reorientation induced by electric field plays a significant role on the structures of confined water inside and outside SWCNTs. Inside SWCNTs, the average water occupancy and the average number of hydrogen bonds(H-bonds) per water molecule decrease as the electric intensity increases. Because the field intensity is sufciently strong, the initial water structures inside the SWCNTs are destroyed, and the isolated water clusters are found. Outside SWCNTs, the azimuthal distributions of the density and the average number of H-bonds per water molecule around the solid walls become more and more asymmetric as the electric intensity increases. The percentages of water molecules involved in 0–5 H-bonds for all the three types of SWCNTs under diferent field intensities are displayed. The results show that those water molecules involved with most H-bonds are the most important to hold the original structures. When the electric field direction is parallel with the original preferred orientation, the density and the H-bond connections in water will be increased; when the electric field direction is perpendicular to the original preferred orientation, the density and the H-bond connections in water will be decreased.