Dipole Polarization Effects Research Articles

Determination of Dipole Polarization Effects in 7Li and 11Li

The structure of 6Li, 7Li and 11Li nuclei is investigated in a model space which includes all configurations with oscillator energy up to 3hω above the ground state configuration. The energy spectra and electromagnetic properties of the low-lying states are determined with various two-body interactions, which are derived from the Bonn potential. In addition the calculation determines the dipole polarizability of7 Li and 11Li caused from virtual E1 excitations to the positive parity states of these nuclei.

Donor–Acceptor Porous Conjugated Polymers for Photocatalytic Hydrogen Production: The Importance of Acceptor Comonomer

Porous conjugated polymer (PCP) is a new kind of photocatalyst for photocatalytic hydrogen production (PHP). Here, we report the importance of the electronic properties of acceptor comonomer in determining the reactivity of 4,8-di(thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene (DBD)-based PCP photocatalyst for PHP application. It was found that the incorporation of nitrogen-containing ligand acceptor monomers into PCP network is an effective strategy to enhance the PHP activity. These moderately electron-deficient comonomers enhanced the dipole polarization effect. These PCPs exhibit appropriate solid-state morphology for charge transport. Powder X-ray diffraction (XRD) studies demonstrate that these PCP materials are semicrystalline materials. A strong correlation between the crystalline property and PHP activity is observed. The replacement of nitrogen-containing ligand acceptors with ligand-free strong acceptors is proved to be detrimental to the PHP process, indicating the proper choice in the electroni...

Investigation of Coulomb dipole polarization effects on reactions involving exotic nuclei

We have analyzed elastic scattering angular distributions and total reaction cross sections of the exotic nuclei $^{9,11}\text{Li}$ on $^{208}\text{Pb}$, at energies below and above the Coulomb barrier. For this purpose, we have used an optical potential with no adjustable parameters, composed by the nuclear S\~ao Paulo potential, derived from the nonlocal nature of the interaction, and the Coulomb dipole polarization potential, derived from the semiclassical theory of Coulomb excitation. Within this formalism, we identified an unusual long-range absorption for the $^{11}\text{Li}+^{208}\text{Pb}$ system, which is dominated by the Coulomb interaction. We compare it to the absorption mechanisms observed for $^{6}\text{He}+^{208}\text{Pb}$ which, unlike those of $^{11}\text{Li}+^{208}\text{Pb}$, take place at small interacting distances, where both Coulomb and nuclear interactions are important. The proposed approach shows to be a fundamental basis to study reactions involving exotic nuclei.

Molecular dynamics simulation of the thermodynamic and transport properties of the molten salt fast reactor fuel LiF–ThF4

The local structure and transport properties of molten LiF–ThF4 at the eutectic composition have been studied at a range of temperatures, using molecular dynamics simulations that incorporate dipole polarization effects. This polarizable interaction potential was parameterized from first-principles calculations. We have calculated the density, self-diffusion coefficients, electrical conductivity, viscosity, and heat capacity at a range of temperatures from 850K to 1273K. We have also examined the changes in coordination number as a function of temperature. The simulation results were in good agreement with available experimental data, indicating that such simulations can fulfill a valuable role in augmenting existing experimental work.

ChemInform Abstract: Including Many‐Body Effects in Models for Ionic Liquids

AbstractReview: 124 refs.

Including many-body effects in models for ionic liquids

Realistic modeling of ionic systems necessitates taking explicitly account of many-body effects. In molecular dynamics simulations, it is possible to introduce explicitly these effects through the use of additional degrees of freedom. Here we present two models: The first one only includes dipole polarization effect, while the second also accounts for quadrupole polarization as well as the effects of compression and deformation of an ion by its immediate coordination environment. All the parameters involved in these models are extracted from first-principles density functional theory calculations. This step is routinely done through an extended force-matching procedure, which has proven to be very succesfull for molten oxides and molten fluorides. Recent developments based on the use of localized orbitals can be used to complement the force-matching procedure by allowing for the direct calculations of several parameters such as the individual polarizabilities.

Theoretical study of the Rydberg series energy levels of ns2S1/2,np2P1/2,3/2, nd2D3/2,5/2 and nf2F5/2,7/2 for alkali-metal Li, Na, K, Rb, Cs and Fr

In the frame work of multi-channel quantum defect theory, the energy levels of Rydberg series of ss2S1/2, np2P1/2, np2P3/2, nd2D3/2, nd2D5/2, nf2F5/2 and nf2F7/2 of alkali-metal atom are calculated by the relativistic multi-channel theory, in five different approximations, i.e., frozen core approximation, with consideration of l=-1 dipole polarization effect, l=+1 dipole polarization effect, l = 1 dipole polarization effect, stretch effect, and both dipole polarization effects and stretch effect, respectively. The present calculations show that electron correlation effect plays an important role in the energy level of Rydberg series. In summary, dipole polarization effect is more important than the stretch effect, and the l = + 1 dipole polarization effect is more important than l = - 1 dipole polarization effect. However, stretch effect is more important for energy levels of both Rydberg series ns2S1/2,(nd2D3/2,nd2D5/2) of Na, and Rydberg series (np2P1/2,np2P3/2) of Li.

Studies of AC conductivity and dielectric relaxation behavior of CdO‐doped nanometric polyaniline

AbstractThe Cadmium oxide doped in nanocrystalline polyaniline (CdO/PANI) composite were prepared with various weight percentages by in situ polymerization method using aniline, ammonium per sulfate, and CdO as starting materials. The frequency dependent conductivity and dielectric behavior of PANI/CdO composites have been studied. The formation of nano PANI and PANI/CdO composites with regards to the structural and microstructural properties of the materials were investigated by XRD, FTIR, and SEM techniques. The variation of σac with frequency obeys Jonscher power law except a small deviation in the low frequency region and is due to dipole polarization effect. The σac increases with increase in CdO concentration. Studies of dielectric properties at lower frequencies show that the relaxation behavior is superimposed by dipole polarization effect. The appearance of peak for each concentration in the loss tangent suggests the presence of relaxing dipoles in the PANI/CdO composite. On addition of CdO, the peak shifts toward higher frequency side indicating the speed up of the relaxation time. Analysis of frequency dependent dielectric suggests that the electronic and polymer segmental motions are strongly coupled. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Modification of spontaneous emission from nanodiamond colour centres on a structured surface

Colour centres in diamond are promising candidates as a platform for quantum technologies and biomedical imaging based on spins and/or photons. Controlling the emission properties of colour centres in diamond is a key requirement for the development of efficient single-photon sources having high collection efficiency. A number of groups have achieved an enhancement in the emission rate over narrow wavelength ranges by coupling single emitters in nanodiamond crystals to resonant electromagnetic structures. In this paper, we characterize in detail the spontaneous emission rates of nitrogen-vacancy centres at various locations on a structured substrate. We found a factor of 1.5 average enhancement of the total emission rate when nanodiamonds are on an opal photonic crystal surface, and observed changes in the lifetime distribution. We present a model for explaining these observations and associate the lifetime properties with dipole orientation and polarization effects.

Frequency splitting of a multi-layered electric ring resonator

We present experimental results on the multilayering effects of an electric ring resonator. The electromagnetic response of the electric ring resonator is measured via a scattering matrix using a vector network analyzer at the X-band frequency. Structures of the electric ring resonator with up to four layers were tested and analyzed using commercial software. We demonstrate that, in an electric ring resonator, the electric and magnetic dipole polarization effect gives rise to resonance frequency splitting when the cell is multilayered.

STUDY OF IONIC CONDUCTIVITY IN CUBIC CERIA BY THE STATISTICAL MOMENT METHOD

We have investigated the diffusion and ionic conductivity of the cubic ceria CeO 2 using the statistical moment method (SMM) in the statistical physics. The activation energy, diffusion coefficient, pre-exponential factor and ionic conductivity are derived in closed analytic forms. The SMM calculations are performed by using the Buckingham potential for the cubic ceria. The effects of the three different potential parameter sets of the Buckingham potential and influence of dipole polarization effects on activation energy, diffusion coefficient and ionic conductivity for CeO 2 are also investigated. The present analytical formulas including the anharmonic effects of the lattice vibrations give the predicted values of these quantities, which are comparable to those of the experimental values.

The role of exact‐exchange in the theoretical description of organic‐metal interfaces

AbstractWe investigate the ability of different density functional methods to describe the electronic properties of isolated gold clusters, self‐assembled monolayers (SAM) of oligophenylthiols (including the depolarization effect), and the biphenylthiol/gold interface. To elucidate the role of the exchange interaction, we consider a hierarchy of functionals including conventional (e.g., within the gradient corrected approximation), hybrid, and effective exact‐exchange functionals, namely the Localized Hartree–Fock (LHF) method, which is free from the self‐interaction‐error (SIE).We find that conventional exchange‐correlation functionals cannot well describe the energy‐level alignment at the metal/organic interface and predict a negligible metal‐molecule charge‐transfer. In addition, an overestimation of dipole moments and polarization effects are obtained in oligophenylthiols, leading to a wrong description of the SAM depolarization effect. Both limitations are mostly overcome if exact‐exchange contributions are taken into account either using an hybrid functional or the LHF method. In particular, an accurate description of the metal/organic interface is only achieved using SIE free methods. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

Relativistic multichannel treatment of the autoionization Rydberg series 3ds(1D2)np 2Po1/2 of scandium

In the framework of multichannel quantum defect theory, the energy levels of autoionization Rydberg series of 3ds(1D2)np (n = 13–21) 2Po1/2 of scandium (Sc) are calculated from first principles by relativistic multichannel theory, and these calculations are at four levels of approximation, i.e. frozen core approximation, including dipole polarization effects, quadrupole polarization effects and both dipole polarization and quadrupole polarization effects, respectively. The present calculations show that both dipole polarization and quadrupole polarization effects play an important role. The calculation that includes both dipole polarization effects and quadrupole polarization effects agrees well with the experimental data. Furthermore, two perturbed states related to quadrupole polarization effects are found in the energy region of autoionization Rydberg series of of Sc and assigned based on our calculation.

Theoretical study of autoionization Rydberg series 3d4s(1D2)nf2 D3/2,3d4s(1D2)nf2 F5/2 and 3d4s(1D2</s

In the frame work of multi-channel quantum defect theory, the energy levels of three autoionization Rydberg series converging to Sc+ 3d4s(1D2) with Jπ=(3/2)-,(5/2)- are calculated from first principles by relativistic multi-channel theory at two levels of approximation, i.e., frozen core approximation and that with consideration of dipole polarization. Considering dipole polarization effect, the difference between calculated and experimental quantum defects for the 3d4s(1D2)np2D3/2 and 3d4s(1D2)nf2F5/2 series are smaller than 0.01, thus the dipole polarization effects are important for the two autoionization Rydberg series. While for 3d4s(1D2)nf2D3/2 series, the calculated data by frozen core approximation are close to those by considering dipole polarization effects, and the difference between calculated and experimental quantum defects are generally about 0.04.

The construction of a reliable potential for GeO2 from first principles

The construction of a reliable potential for GeO2 from first principles is described. The obtained potential, which includes dipole polarization effects, is able to reproduce all the studied properties (structural, dynamical and vibrational) to a high degree of precision with a single set of parameters. In particular, the infrared spectrum was obtained using the expression proposed for the dielectric function of polarizable ionic solutions reported by Weis et al. [J. Chem. Phys. 91, 5544 (1989)]. The agreement with the experimental spectrum is very good, with three main bands that are associated with tetrahedral modes of the GeO2 network. Finally, we give a comparison with a simpler pair-additive potential.

Relativistic multichannel treatment of autoionization Rydberg series of 4s2nf(n = 4 − 23) Jπ = (7/2)° for scandium

Based on relativistic multichannel theory, this paper calculates the energy levels of autoionization Rydberg series 4s2nf(n = 4 − 23)Jπ = (7/2)° of scandium at different levels of approximation within the framework of multichannel quantum defect theory. The present results show that the dipole polarizations play an important role. Considering the dynamical dipole polarization effects, this paper finds that the difference between calculated and experimental quantum defects for the 4s2nf(n = 4 − 23)Jπ = (7/2)° series is generally about 0.01–0.03. Furthermore, the reason that 4s216f is obscured in experimental spectra is suggested to be the interaction with the neighbouring resonance state converged to 3d2(1G4)of Sc+.

Investigation of thermodynamic properties of cerium dioxide by statistical moment method

The thermodynamic properties of the cerium dioxide (CeO2) are studied using the statistical moment method, including the anharmonicity effects of thermal lattice vibrations. The free energy, linear thermal expansion coefficient, bulk modulus, specific heats at the constant volume and those at the constant pressure, CV and CP, are derived in closed analytic forms in terms of the power moments of the atomic displacements. The temperature dependence of the thermodynamic quantities of cerium dioxide is calculated using three different interatomic potentials. The influence of dipole polarization effects on the thermodynamic properties and thermodynamic stability of cerium dioxide have been studied in detail.

Fast electron correlation methods for molecular clusters in the ground and excited states*

An efficient and accurate electronic structure method for clusters of weakly interacting molecules has been proposed, on the basis of the pair-interaction method of Kitaura et al., and combined with density functional, many-body perturbation, coupled-cluster, equation-of-motion coupled-cluster, configuration-interaction singles, and time-dependent density functional theories. The method retains the one- and two-body (and, if necessary, also three-body) Coulomb, exchange, and correlation energies exactly and higher-order Coulomb energies in the leading order of multipole expansion (hence the dipole polarization or induction effects). The latter makes the combination of this method with existing implementations of any electronic structure theory extremely easy. It typically recovers the total energies within 0.001%, binding energies within a few kilocalories per mole, and excitation energies within a few hundredths of an electron volt of the conventional implementations. The size dependence of the computational cost of the method is asymptotically linear for total energies and constant for excitation energies. The method has been applied to the total energies of water clusters, to the total energies of zwitterionic and neutral glycine–water clusters, and to the excitation energies of formaldehyde–water clusters. The largest calculation was performed at an equation-of-motion coupled-cluster singles and doubles level for a formaldehyde–(H2O)81 cluster containing 247 atoms that predicted the solvatochromic shift of 1360 cm−1 in the lowest transition energy of formaldehyde in water.

Image dipole approach and polarization effects in scanning near-field optical microscopy

A coupled-dipole approach is proposed in order to study the coupling between the probe tip and the rough sample in SNOM. In the present model both the optical probe tip and the sample protrusions are represented by polarizable dipole spheres. The induced polarization effects on the sample surface can be replaced by the image dipoles in the circumstance of quasi-static electromagnetic field approximation. Applying the radiation theory of the dipole, we have established a set of self-consistent equations to describe the field distribution at the sites of the probe tip and the sample protrusions. The results are completely the same as those obtained by means of the dyadic electromagnetic propagator formalism and also the derivation procedure is relatively simple. This method permits us to analyze the physical mechanisms of the interaction between the probe tip and the rough surface in SNOM intuitively. Based on this approach, we further discuss the influence of polarization of the incident light on the imaging quality. The calculating result shows that the shape and the contrast of the images of the sample are both sensitive to the field polarization, and the z-polarized mode is proved to give better resolution in SNOM.

Multipoles and interaction potentials in ionic materials from planewave-DFT calculations.

Oxide potentials which transfer well between different materials have to account explicitly for many-body contributions to the interaction potentials between the ions. These include dipole and quadrupole polarization effects and the compression and deformation of an oxide ion by its immediate coordination environment. Such complex potentials necessarily involve many parameters. We examine how the results of ab initio electronic structure calculations, based upon planewave DFT methods, on general configurations of ions derived from simulations at finite temperature, may be used to parameterize an "aspherical ion method" (AIM) potential (A. J. Rowley, P. Jemmer, M. Wilson and P. A. Madden, J Chem. Phys., 1998, 108, 10209). Dipoles and quadrupoles on the individual ions are obtained via a transformation of the Kohn Sham orbitals to localized orbitals on each ion, which enables a distorted charge density for each ion to be obtained. The dipoles and quadrupoles appearing in polarization parts of the AIM potential are fit to those obtained from the ab initio ionic charge densities obtained in this way. The remaining parts of the potential, describing short-range repulsive interactions between ions with compressed and deformed charge densities, are fit to the ab initio forces and the stress tensor. By using a sufficiently large and varied set of configurations on which to carry out this optimization, an excellent transferable potential is obtained.