Account Polarization Effects Research Articles

Electret-thermal analysis of dielectric objects

The development of methodological tools for studying the most possible range of the objects of dielectric nature is an urgent task. We present the results of studying dielectric objects by the method of electret-thermal analysis (ETA). Electrophysical changes in dielectric objects were studied taking into account polarization effects and electret state. The ETA data of ultrahigh molecular polyethylene, polyvinyl alcohol, human blood, synovial fluid, starch-containing polymer biodegradable compositions, chitosan, and vegetable oils are presented. Analysis of the spectra of thermally stimulated currents obtained during tests revealed that ETA method is characterized by high information content regarding various dielectric objects.Thermally stimulated current response makes it possible to identify and interpret phase phenomena occurring upon heating of the objects, including those accompanied by electrophysical processes of transfer and relaxation of the electret charge. The results obtained can be used to improve the methodology for analyzing electrophysical changes in dielectric objects.

Upgraded AMBER Force Field for Zinc-Binding Residues and Ligands for Predicting Structural Properties and Binding Affinities in Zinc-Proteins.

We developed a novel force field in the context of AMBER parameterization for glutamate and aspartate zinc(II)-binding residues. The interaction between the zinc ion and the coordinating atoms is represented by a spherical nonbonded parameterization. The polarization effect due to the zinc ion has been taken into account by redefining the atomic charges on the residues through accurate quantum mechanical calculations. The new zinc-binding ASP and GLU residues, along with the CYS and HIS zinc-binding residues, parameterized in a recent work [MacchiagodenaM.;J. Chem. Inf. Model.2019, 59, 3803−381631385702], allow users to reliably simulate 96% of the Zn-proteins available in the Protein Data Bank. The upgraded force field for zinc(II)-bound residues has been tested performing molecular dynamics simulations with an explicit solvent and comparing the structural information with experimental data for five different proteins binding zinc(II) with GLU, ASP, HIS, and CYS. We further validated our approach by evaluating the binding free energy of (R)-2-benzyl-3-nitropropanoic acid to carboxypeptidase A using a recently developed nonequilibrium alchemical method. We demonstrated that in this setting it is crucial to take into account polarization effects also on the metal-bound inhibitor.

Improved Force Field Model for the Deep Eutectic Solvent Ethaline: Reliable Physicochemical Properties

In this work, we combined various parameters found in the literature for the choline cation, chloride anion, and ethylene glycol to set up force field models (FFMs) for a eutectic mixture, namely, ethaline (1:2 choline chloride/ethylene glycol (ChCl:2EG)). The validation of these models was carried out on the basis of physical and chemical properties, such as the density, expansion coefficient, enthalpy of vaporization, self-diffusion coefficients, isothermal compressibility, surface tension, and shear viscosity. After the initial evaluation of the FFMs, a refinement was found necessary and accomplished by taking into account polarization effects in a mean-field manner. This was achieved by rescaling the electrostatic charges of the ions based on partial charges derived from ab initio molecular dynamics (MD) simulations of the bulk system. Classical all-atom MD simulations performed over a large range of temperatures (298.15-373.15 K) using the refined FFMs clearly showed improved results, allowing a better prediction of experimental properties. Specific structural properties (radial distribution functions and hydrogen bonding) were then analyzed in order to support the adequacy of the proposed refinement. The final selected FFM leads to excellent agreement between simulated and experimental data on dynamic and structural properties. Moreover, compared to the previously reported force field model (Perkins, S. L.; Painter, P.; Colina, C. M. Experimental and Computational Studies of Choline Chloride-Based Deep Eutectic Solvents. J. Chem. Eng. Data 2014, 59, 3652-3662), a 10% improvement in simulated transport properties, i.e., self-diffusion coefficients, was achieved. The isothermal compressibility, surface tension, and shear viscosity for ethaline are accessed in MD simulations for the first time.

High‐efficiency indium gallium nitride/Si tandem photovoltaic solar cells modeling using indium gallium nitride semibulk material: monolithic integration versus 4‐terminal tandem cells

AbstractIn this work, we present a double‐junction solar cell with a crystalline silicon solar cell as a bottom junction and an indium gallium nitride‐based semibulk‐structured solar cell as a top junction. Using SILVACO Atlas and taking into account polarization effects in III‐N materials, we have shown that 50% of indium is needed to ensure the current matching between the top cell and the bottom cell in 2‐terminal configuration. Such high indium composition is technologically challenging to grow. Thus, we have also modeled a 4‐terminal configuration showing the same performance (i.e. conversion efficiency close to 29%) where only 25% of indium content is needed. Copyright © 2016 John Wiley & Sons, Ltd.

Many-electron correlations in computations of sodium atom photoabsorption

The role of many-electron correlations in photoabsorption processes has been investigated. The results of numerical computations of photoionization cross sections of sodium atom are presented. The many-body effects such as interchannel correlations resulting in autoionization resonance peaks, as well as effects of atomic core polarization were taken into account in the computations in terms of RPAE. Polarization corrections were accounted for using both static and dynamic polarization potentials. The influence of correlations on the position and the form of resonance peaks was studied. The obtained results demonstrate necessity of taking into account polarization effects, especially for clarification of autoionization resonance peaks position and the cross-section magnitudes in the low energy range. The best agreement with experimental data was reached with the model of dynamic polarization potential based on Dyson equation.

Effect of Polarization on the Mobility of C60: A Kinetic Monte Carlo Study.

We present a study of mobility field and temperature dependence for C60 with Kinetic Monte Carlo simulations. We propose a new scheme to take into account polarization effects in organic materials through atomic induced dipoles on nearby molecules. This leads to an energy correction for the single site energies and to an external reorganization happening after each hopping. The inclusion of polarization allows us to obtain a good agreement with experiments for both mobility field and temperature dependence.

A Variational Approach to Electrostatics of Polarizable Heterogeneous Substances

We discuss equilibrium conditions for heterogeneous substances subject to electrostatic or magnetostatic effects. We demonstrate that the force-like aleph tensorℵijand the energy-like beth tensorℶijfor polarizable deformable substances are divergence-free:∇iℵij=0and∇iℶij=0. We introduce two additional tensors: the divergence-free energy-like gimel tensorℷijfor rigid dielectrics and the general electrostatic gamma tensorΓijwhich is not divergence-free. Our approach is based on a logically consistent extension of the Gibbs energy principle that takes into account polarization effects. While the model is mathematically rigorous, we caution against the assumption that it can reliably predict physical phenomena. On the contrary, clear models often lead to conclusions that are at odds with experiment and therefore should be treated as physical paradoxes that deserve the attention of the scientific community.

Statistical description of hydrodynamic processes in ionic melts while taking into account polarization effects

A statistical description of hydrodynamic processes for molten salts is proposed taking into account polarization effects caused by the deformation of external ionic shells. This description is conducted by means of the Zubarev nonequilibrium statistical operator method, appropriate for researches of both strong and weak nonequilibrium processes. The nonequilibrium statistical operator and the generalized hydrodynamic equations that take into account the polarization processes are acquired for the ion-polarization model of ionic molten salts when the nonequilibrium averaged values of densities of ions number, their momentum, dipole momentum, and total energy are chosen for the reduced description parameters. A spectrum of collective excitations is investigated within the viscoelastic approximation for the ion-polarization model of ionic melts.

Radiative and non-radiative local density of states on disordered plasmonic films

We present numerical calculations of the local density of optical states (LDOS) in the near field of disordered plasmonic films. The calculations are based on an integral volume method, that takes into account polarization and retardation effects, and allows us to discriminate radiative and non-radiative contributions to the LDOS. At short distance, the LDOS fluctuations are dominated by non-radiative channels, showing that changes in the spontaneous dynamics of dipole emitters are driven by non-radiative coupling to plasmon modes. Maps of radiative and non-radiative LDOS exhibit strong fluctuations, but with substantially different spatial distributions.

Numerical calculation of electronic states in ellipsoidal finite-potential quantum dots with an off-centered impurity

In this article, the computational procedure to calculate wave-functions and energies of spherical quantum dots with finite barriers and a shallow donor impurity located anywhere inside is extended to prolate spheroidal quantum dots. As in the spherical case, the extension of the procedure fully takes into account polarization effects originating from the dielectric mismatch at the dot surface. Particular attentions are paid to the calculations of self-polarization potential energy so as to overcome the mathematical divergence in the self energy when the sharp step-like dielectric interface is assumed between the dot and the surrounding matrix. In this regard, the so-called three-layer dielectric models, including the novel quasi-harmonic dielectric model, are employed. The procedure is implemented to calculate energy states of a prolate spheroidal quantum dot with a hydrogenic donor impurity located at the polar axis of the dot, held at a finite confining potential. The resulting code is then employed to carry out an illustrative study on the effects of the dielectric mismatch, the impurity location, and the choice of dielectric models to the electronic energy in the dot.

High‐Throughput Virtual Screening Using Quantum Mechanical Probes: Discovery of Selective Kinase Inhibitors

A procedure based on semi-empirical quantum mechanical (QM) calculations of interaction energy is proposed for the rapid screening of compound poses generated by high-throughput docking. Small molecules (consisting of 2-10 atoms and termed "probes") are overlapped with polar groups in the binding site of the protein target. The interaction energy values between each compound pose and the probes, calculated by a semi-empirical Hamiltonian, are used as filters. The QM probe method does not require fixed partial charges and takes into account polarization and charge-transfer effects which are not captured by conventional force fields. The procedure is applied to screen approximately 100 million poses (of 2.7 million commercially available compounds) obtained by high-throughput docking in the ATP binding site of the tyrosine kinase erythropoietin-producing human hepatocellular carcinoma receptor B4 (EphB4). Three QM probes on the hinge region and one at the entrance pocket are employed to select for binding affinity, while a QM probe on the side chain of the so-called gatekeeper residue (a hypervariable residue in the kinome) is used to enforce selectivity. The poses with favorable interactions with the five QM probes are filtered further for hydrophobic matching and low ligand strain. In this way, a single-digit micromolar inhibitor of EphB4 with a relatively good selectivity profile is identified in a multimillion-compound library upon experimental tests of only 23 molecules.

A stable complex Jacobi iterative solution of 3D semivectorial wide-angle beam propagation using the iterated Crank–Nicholson method

An extension of the recently proposed three-dimensional (3D) wide-angle (WA) beam propagation method (BPM) using complex Jacobi iteration (CJI) taken into account polarization effects is presented. The resulting iterative BPM is faster than BPMs based on the traditional direct matrix inversion for waveguides with unchanging refractive index profiles during propagation direction. However, for varying refractive index waveguides the iterative method suffered from the fact that the iteration count between two successive cross-sections increases dramatically during the propagation direction. To overcome this problem, we propose the utility of the iterated Crank-Nicholson method. At each propagation step, the propagation equation is divided in multiple stages by the iterated Crank-Nicholson method and then each stage is recast in terms of a Helmholtz equation with source term, which is solved effectively by the complex Jacobi iterative method. The resulting approach is stable and well-suited for large structures with long propagation paths.

Electromodulation spectroscopy of the ground and excited state transitions in GaInN/AlInN multi-quantum wells

Contactless electroreflectance (CER) has been applied to investigate energies and intensities of optical transitions in GaInN/AlInN multi-quantum wells (MQWs) with the various QW widths (1.55 and 1.8nm) and barrier thicknesses (3 and 6nm). In addition to the ground state transition, optical transitions related to excited states (2H–1C and 1H–2C transitions, where kH–lC denotes a transition between the kth valence and the lth conduction subbands) have been observed in CER spectra. It has been found that the intensities of 2H–1C and 1H–2C transitions (i.e., transitions which are forbidden for non-polar square-like QWs) are comparable with the intensity of the ground state transition. In addition, it has been observed that the relative intensities of QW transitions depend on both the QW width as well as the barrier thickness. This experimental observation has been confirmed by theoretical calculations performed in the framework of the electron effective mass approximation model taking into account polarization effects in wurtzite III-N alloys. The calculations clearly show that the intensity of QW transitions for GaInN/AlInN MQWs strongly varies with the QW width as well as the barrier thickness.

Is Quantum Mechanics Necessary for Predicting Binding Free Energy?

To take into account polarization effects, the linear interaction energy model with continuum electrostatic solvation (LIECE) is supplemented by the linear-scaling semiempirical quantum mechanical calculation of the intermolecular electrostatic energy (QMLIECE). QMLIECE and LIECE are compared on three enzymes belonging to different classes: the West Nile virus NS3 serine protease (WNV PR), the aspartic protease of the human immunodeficiency virus (HIV-1 PR), and the human cyclin-dependent kinase 2 (CDK2). QMLIECE is superior for 44 peptidic inhibitors of WNV PR because of the different amount of polarization due to the broad range of formal charges of the inhibitors (from 0 to 3). On the other hand, QMLIECE and LIECE show similar accuracy for 24 peptidic inhibitors of HIV-1 PR (20 neutral and 4 with one formal charge) and for 73 CDK2 inhibitors (all neutral). These results indicate that quantum mechanics is essential when the inhibitor/protein complexes have highly variable charge-charge interactions.

FDTD-based time reversal for microwave breast cancer Detection-localization in three dimensions

In a previous study, a novel time-reversal (TR) algorithm based on the finite-difference time-domain (FDTD) method for ultra-wideband microwave breast cancer detection was presented. The system properties and performance were originally studied for two-dimensional (2-D) simplified models and geometries and, more recently, for a realistic breast model based on magnetic resonance imaging measured data. This paper extends this FDTD TR algorithm to a three-dimensional (3-D) case in order to study localization of the tumor target in 3-D. The FDTD TR algorithm solves the full 3-D wave equation and, thus, takes into account polarization effects. In order to compare the new images with previous results, we consider a 2-D planar receiver array, which is an extension of the line of receivers introduced in the 2-D model. A direct comparison from 3-D to 2-D reconstructions illustrates the advantages of using the fully 3-D algorithm, which counterbalances its additional computational cost.

Capacitance characterization of AlN/GaN double‐barrier resonant tunnelling diodes

AbstractWe report on the electrical characterization of AlN/GaN/AlN double‐barrier resonant tunnelling diodes (RTDs) using steady‐state current‐voltage and capacitance‐voltage (C‐V) characteristics in a wide frequency range with 2 kHz steps. The C‐V characteristics of a double‐barrier RTD show different behaviour under forward and reverse polarities and a strong dependence on frequency. The monotonous growth of capacitance at forward bias was registered, while a more complicated dependence was observed at reverse voltages. In order to analyse this dependence, a self‐consistent calculation of the potential profile of the structure was performed taking into account polarization effects at the AlN/GaN interfaces. The peculiarities are analysed in the model of possible charge trapping at the interface states. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of inhomogeneous surface albedo on diffuse UV sky radiance at a high‐altitude site

Situated at the very edge of the Aletsch Glacier and thus at the boundary between snow‐covered and snow‐free terrain, the High Alpine Research Station Jungfraujoch (Switzerland, 3576 m above sea level) represents an ideal site for experimental quantification of surface albedo effects on solar UV radiation. Monochromatic measurements of directional radiance distribution in the sky, performed with a 1° aperture lens optics at 310 nm and 350 nm under cloudless sky conditions, are compared with discrete ordinate model calculations of corresponding data over homogeneously snow‐covered terrain, taking into account polarization effects for an aerosol‐free atmosphere. The model agrees within ±5% with radiance measurements at the forward scattering direction of the principal plane toward southeast, where snow‐covered terrain dominates. Toward northwest, the effect of snow‐free terrain causes a significant reduction of UV sky radiance at the backward scattering direction of the principal plane relative to the modeled situation with homogeneous snow cover. Depending on the actual solar zenith angle, this reduction amounts to between 20% and 40%.

Local microstructure of Ge layers buried in a silicon crystal studied by extended X-ray absorption fine structure

The local structure of Si-capped Ge quantum dots formed in Stranski–Krastanov growth mode on a (001) Si substrate was probed by X-ray absorption at the Ge K-edge. Analysis by extended X-ray absorption fine structure (EXAFS) was performed under the assumption of a solid solution model of the Si distribution inside the quantum dots (QDs) and taking into account polarization effects. It was found that QDs formed for 8 ML are strained and the Ge–Ge and Ge–Si bond lengths vary with direction. The Si content inside the QDs was found to be at a level of ∼25 at.% for strained (8 ML sample) QDs and ∼12 at.% for unstrained (10 ML sample) QDs. This work demonstrates the usefulness of EXAFS analysis for the determination of the local atomic structure in covered low-dimensional structures.

Optical scanning holography as a technique for high-resolution three-dimensional biological microscopy.

The applicability of optical scanning holography (OSH) to the field of microscopic imaging for biological applications is assessed. A generalized mathematical description of OSH that takes into account polarization effects, high numerical apertures, and generalized illumination wave fronts is presented. This description is used to show that the proposed single-beam scanning technique relaxes the restrictions under which OSH functions correctly compared with the conventional double-beam scanning method. It is also shown that, although in general OSH is restricted to thin samples, this condition can be relaxed in nonrefracting fluorescence samples, which are of importance in biological microscopy.

Polarization mechanism for bremsstrahlung and radiative recombination in a plasma with heavy ions

The role of the polarization mechanism in bremsstrahlung and radiative recombination in a plasma with heavy ions is investigated. A study is made of a hot plasma with the electron temperature Te=0.5 keV, containing Fe, Mo, W, and U ions, a relatively cold plasma with a temperature of 0.1–10 eV, and a storage-ring plasma with relatively low-energy electrons. The spectral characteristics, as well as the total cross sections and rate constants for electron-ion recombination, are calculated with allowance for real ionization equilibrium in a plasma. The calculations are carried out using the quasiclassical approximation for electron scattering and the statistical model for the ions, which provides a universal description of the spectra of various chemical elements over a wide temperature range. It is shown that the polarization mechanism contributes to both the effective radiation intensity and the total radiative recombination rate. The temperature range is found where the polarization recombination of electrons in collisions with FeIII ions plays an important role, which indicates the collective behavior of the electron core of an iron ion in this temperature range. Taking into account polarization effects increases the calculated total continuum intensity. As a consequence, the effective plasma charge Zeff determined from this intensity without allowance for polarization effects turns out to be overestimated.