Induced Dipole Moment Research Articles

Two-dimensional colloidal networks induced by a uni-axial external field

Based on Monte Carlo and Molecular Dynamics computer simulations we investigate the aggregation patterns and dynamics of model colloidal mixtures consisting of particles with either one or two, oppositely oriented, induced dipole moments. The mixtures are confined to two spatial dimensions. Our model is inspired by recent optical-microscopy experiments involving polystyrene particles with (and without) gold patches. For a broad range of parameters, we find the model systems to self-assemble via a two-step scenario involving first percolation along the field, followed by a percolation transition in the transverse direction. The resulting two-dimensional networks are characterized by strongly hindered translational dynamics.

First-principles study on the piezoelectric properties of hydrogen modified graphene nanoribbons

This paper focuses on the piezoelectric properties of zigzag graphene nanoribbons with hydrogen selective modifications by first-principles calculations. The structures of hydrogen modified graphene nanoribbons are optimized and the calculated hydrogen binding energies indicate that these structures are very stable. Owing to the hydrogen atom selective adsorption, the adjacent carbon atoms have different charge states and breaking inversion symmetries of nonpiezoelectric graphene. So, the positive charge centers and the negative charge centers of the hexatomic carbon ring in these structures separate from each other under uniaxial tensile strain, inducing the macroscopical electric polarization. Furthermore, the gradient of strain induced dipole moment density is related to ribbon width, i.e., the wider the ribbon, the better the piezoelectric property is. Besides, the dipole moment density of hydrogen selective modified graphene nanoribbons without strain could be controlled by changing the edge modification configuration of hydrogen atoms effectually.

Self-organised aggregation of a pair of particles with different resonant frequencies and electric dipole moments of transitions, controlled by an external quasi-resonant field

The influence of the oscillation phases of the dipole moments induced in metal nanoparticles and quantum dots by an external laser field on their interaction energy is considered. It is shown that a difference in resonant frequencies leads to the formation of additional minima and maxima, which are absent in the spectral dependence of the interaction energy of identical particles at similar orientations of the pair of particles with respect to the plane of polarisation of radiation. These features are due to the fact that the oscillation phase difference of the induced dipole moments of particles reaches values close to .

Positron-attachment to nonpolar or small dipole CXY (X, Y = O, S, and Se) molecules: vibrational enhancement of positron affinities with configuration interaction level of multi-component molecular orbital approach

To theoretically demonstrate the binding of a positron to a nonpolar or small dipole molecule, we have calculated the vibrational averaged positron affinity (PA) values along the harmonic asymmetric stretching vibrational coordinate with the configuration interaction level of multi-component molecular orbital method for CXY (X, Y = O, S, and Se) molecules. For CSe2 and CSSe molecules, a positron can even be attached at the equilibrium structures, due to the effect of the induced dipole moment with large polarizability values. For a CS2 molecule, the positive PA value is obtained at the lowest vibrational excited state in our scheme. Although there is no direct experimental evidence for the positron-binding to CO2, COS, and COSe molecules, we have predicted positron-binding for these molecules at higher vibrational excited states.

Transport‐based equivalent circuit for semiconductor nanoparticle in terahertz frequency range

By consideration of the physical process of charge carrier motion and lattice polarisation, an equivalent circuit for a semiconductor nano-particle in the terahertz frequency range is obtained. All circuit elements are of electrical nature and can be directly expressed in terms of material parameters. When the generalised admittance of the circuit is multiplied by the intensity of an externally applied field, the total induced dipole moment of the nanoparticle results, which is in good match to that given by field analysis and simulation. The readily obtained polarisability can serve as the basis of analysis for composite structures and aggregates of which the nanoparticle is a constituent.

Studies on free energy of solvation of certain nitrogen containing heterocyclic compounds

Polarizable continuum model has been used to account for solvent effects in binary mixtures containing six nitrogen containing heterocyclic compounds. The solutes considered in the present investigation are chloroindole (CI), bromoindole (BI), 1-chlorobenzo 1,3-diazole (CD), 1-bromobenzo 1,3-diazole (BD), 1-chlorobenzo 1,2,3-triazole (CT) and 1-bromobenzo 1,2,3 triazole (BT). Electrostatic interaction, dispersion and repulsive energies are calculated for these systems. Free energy of solvation of these six solutes in different solvents is theoretically computed and correlated with the physical properties of the solvents. Induced dipole moments are computed for the six molecules in various solvents.

Ion Solvation in Liquid Mixtures: Effects of Solvent Reorganization

Using field-theoretic techniques, we study the solvation of salt ions in liquid mixtures, accounting for the permanent and induced dipole moments, as well as the molecular volume of the species. With no adjustable parameters, we predict solvation energies in both single-component liquids and binary liquid mixtures that are in excellent agreement with experimental data. Our study shows that the solvation energy of an ion is largely determined by the local response of the permanent and induced dipoles, as well as the local solvent composition in the case of mixtures, and does not simply correlate with the bulk dielectric constant. In particular, we show that, in a binary mixture, it is possible for the component with the lower bulk dielectric constant but larger molecular polarizability to be enriched near the ion.

Dielectric constant and induced dipole moment of edible oils subjected to conventional heating

The frequency dependence of dielectric constant, dielectric loss factor and conductivity are studied for five edible oils in the frequency range 100 kHz to 13 MHz at different temperatures using frequency domain spectroscopy. The dielectric constant is found similar for all the samples and in agreement with the previous reports. The dielectric loss is low (<0.01) except for the virgin olive oil with value of 0.05. Dielectric loss peak frequency is at 4 MHz for corn oil and around 5.2 MHz for the others. At this frequency conductivity is of the order of 10-7-10-9 S/cm, and decreases with temperature following the behavior of the dielectric losses. Refractive index, molar and orientation polarization are calculated for all types of oils using novel theory proposed by N. M. Putintsev and D. N. Putintsev [1]. Data show that the orientation polarization contributes to the observed dielectric constant at low temperatures and frequencies. This indicates that the edible oils are not pure nonpolar dielectrics. Induced dipole moments of oils are calculated for 400 kHz and 10 MHz at 300 K and 318 K. The results are discussed and correlated as a function of temperature and frequency to establish their relationship.

Polarizability Matrix Extraction of a Bianisotropic Metamaterial from the Scattering Parameters of Normally Incident Plane Waves

In this paper, a polarizability matrix retrieval method for bianisotropic metamaterials is presented. Assuming that scatterers can be modeled by electric and magnetic pointdipoles located at their centers, the induced dipole moments are analytically related to the normally incident fields, while the scattered fields are also analytically obtained for two individual cases of normal wave incidence. The latter can be combined with the incident fields, to express the desired polarizabilities, with regard to the measured or simulated scattering parameters. In this way, the polarizability matrix can be extracted by solving the resulting non-linear system of equations. The proposed technique is applied to two different split-ring resonator structures and reveals very good agreement with previously reported techniques.

Ab initio investigation on electronic properties of the adenine molecule contacted with gold electrodes: effects of an external electric field

A theoretical investigation using density functional theory is performed on the electronic properties of a model molecular wire under an external electric field (EF), such as electronic structure and geometry. The molecular wire is modeled as 4Au/S-Adenine-S/4Au where Adenine is a base of deoxyribonucleic acid molecule acting as a molecular bridge. According to our results the gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) decreases with exerting low EF. The application of EF may increase the molecular conjugation and the induced dipole moment. Moreover, the spatial distribution of frontier molecular orbitals moves from a fully delocalized form over whole molecular wire to a partially localized in terminal side which is dependent to EF strength. Accumulated natural bond orbital (NBO) charge on Au, S and NH2 group show that there is a close relationship among these factors and HOMO–LUMO gap. We would also expect an ohmic behavior of the current through the model wire.

New insights into collision-induced rototranslational absorption and scattering spectra of gaseous methane at different temperatures

Quantum mechanical lineshapes of collision-induced absorption (CIA) and of collision-induced light scattering (CILS) at different temperatures for gaseous molecular methane are computed using as input theoretical values for induced dipole moments and pair-polarizability anisotropy. The quantum lineshapes of absorption are reproduced accurately by the extended Birnbaum Cohen (EBC) model with the parameters based on certain function of different coefficients for the octopole and hexadecapole mechanisms. For the scattering, the spectrum consists essentially of an intense, purely translational component which includes scattering due to free pairs and bound dimers and of another component due to the induced rotational scattering. This spectrum has been interpreted by means of pair-polarizability terms, which arise from a short range dipole-induced-dipole (DID) with small dispersion corrections and long range interaction mechanism involving higher-order dipole–quadrupole (A) and dipole–octopole (E) polarizabilities. Good agreement between computed and experimental lineshapes of both absorption and scattering is obtained with potential models constructed from thermophysical and transport properties.

Role of alkaline earth metals adsorption on capped single-walled carbon nanotubes based on first-principles calculations

Abstract The adsorption behaviors of alkaline earth metals (AEMs) including Mg, Ca and Sr on capped (5, 5) and (9, 0) single-walled carbon nanotubes (CNTs) are studied systematically using first-principles density functional theory. The optimized geometry, adsorption energy, density of states (DOS), induced dipole moment, and work function of each adatom-CNT system are calculated via VASP in detail. With only s and p orbitals, the interaction between Mg and pristine carbon nanotubes (PCNTs), no matter what chirality they are, is very weak and belongs to physisorption. But Ca and Sr bind more strongly to the cap of PCNTs in chemisorption form because of their complicated orbitals hybridization with CNTs. The transfer charge is analyzed quantitatively based on the Bader theory. Induced dipole moment and work function variation are observed. Especially, the influence of mono-vacancy defect carbon nanotubes (DCNTs) on adsorption properties is also been considered. The results show that adsorption energy is raised because the vacancy defect and the modification of CNTs are significantly different.

CCSD(T) potential energy and induced dipole surfaces for N2–H2(D2): Retrieval of the collision-induced absorption integrated intensities in the regions of the fundamental and first overtone vibrational transitions

The present work aims at ab initio characterization of the integrated intensity temperature variation of collision-induced absorption (CIA) in N(2)-H(2)(D(2)). Global fits of potential energy surface (PES) and induced dipole moment surface (IDS) were made on the basis of CCSD(T) (coupled cluster with single and double and perturbative triple excitations) calculations with aug-cc-pV(T,Q)Z basis sets. Basis set superposition error correction and extrapolation to complete basis set (CBS) limit techniques were applied to both energy and dipole moment. Classical second cross virial coefficient calculations accounting for the first quantum correction were employed to prove the quality of the obtained PES. The CIA temperature dependence was found in satisfactory agreement with available experimental data.

Density maximum and polarizable models of water

To estimate accurately the density of water over a wide range of temperatures with a density maximum at 4 °C is one of the most stringent tests of molecular models. The shape of the curve influences the ability to describe critical properties and to predict the freezing temperature. While it was demonstrated that with a proper parameter fit nonpolarizable models can approximate this behavior accurately, it is much more difficult to do this for polarizable models. We provide a short overview of ρ-T diagrams for existing models, then we give an explanation of this difficulty. We present a version of the BK model [A. Baranyai and P. T. Kiss, J. Chem. Phys. 133, 144109 (2010); and ibid. 135, 234110 (2011)] which is capable to predict the density of water over a wide range of temperature. The BK model uses the charge-on-spring method with three Gaussian charges. Since the experimental dipole moment and the geometry is fixed, and the quadrupole moment is approximated by a least mean square procedure, parameters of the repulsion and dispersive attraction forces remained as free tools to match experimental properties. Relying on a simplified but plausible justification, the new version of the model uses repulsion and attraction as functions of the induced dipole moment of the molecule. The repulsive force increases, while the attractive force decreases with the size of the molecular dipole moment. At the same time dipole moment dependent dispersion forces are taking part in the polarization of the molecule. This scheme iterates well and, in addition to a reasonable density-temperature function, creates dipole distributions with accurate estimation of the dielectric constant of the liquid.

Alkali-earth metal adsorption behaviors on capped single-walled carbon nanotubes based on first-principle calculations

The adsorption behaviors of alkali-earth metals (AEMs) on the capped (5, 5) and (9, 0) carbon nanotubes (CNTs) are investigated using first-principle calculations based on generalized gradient approximation. The optimized geometry, adsorption energy, induced dipole moment, and work function, at two different sites like hexagon and pentagon, of each adatom-CNT system are calculated. The decrease of work functions, variations of Fermi levels and Bader charge transfer, in spite of CNT chirality, has almost the same regularity when the AEMs are adsorbed on the same polygon. The AEMs are off the pentagonal center of the CNTs, while for the hexagon of the CNTs, their most preferred sites are just the top of the rings. In particular, the adsorption energy and work function reduction of the AEMs on hexagon are slightly larger than that on pentagon.

Methane and carbon dioxide adsorption on edge-functionalized graphene: A comparative DFT study

With a view towards optimizing gas storage and separation in crystalline and disordered nanoporous carbon-based materials, we use ab initio density functional theory calculations to explore the effect of chemical functionalization on gas binding to exposed edges within model carbon nanostructures. We test the geometry, energetics, and charge distribution of in-plane and out-of-plane binding of CO(2) and CH(4) to model zigzag graphene nanoribbons edge-functionalized with COOH, OH, NH(2), H(2)PO(3), NO(2), and CH(3). Although different choices for the exchange-correlation functional lead to a spread of values for the binding energy, trends across the functional groups are largely preserved for each choice, as are the final orientations of the adsorbed gas molecules. We find binding of CO(2) to exceed that of CH(4) by roughly a factor of two. However, the two gases follow very similar trends with changes in the attached functional group, despite different molecular symmetries. Our results indicate that the presence of NH(2), H(2)PO(3), NO(2), and COOH functional groups can significantly enhance gas binding, making the edges potentially viable binding sites in materials with high concentrations of edge carbons. To first order, in-plane binding strength correlates with the larger permanent and induced dipole moments on these groups. Implications for tailoring carbon structures for increased gas uptake and improved CO(2)/CH(4) selectivity are discussed.

Polarization-sensitive cathodoluminescence Fourier microscopy

Determining the emission polarization properties of sub-wavelength structures like optical nanoantennas, nanocavities and photonic crystals is important to understand their physical properties and to optimize their use in applications. Recently we have shown that angle-resolved cathodoluminescence imaging spectroscopy (ARCIS), which uses a 30 keV electron beam as an excitation source, is a useful technique to study the far-field properties of such structures. Here we extend the technique with polarization-sensitive angular detection. As proof-of-principle, we experimentally probe the emission polarization properties of three orthogonal dipolar emitters of which the polarization is well-known and find excellent agreement between experiment and theory. We access these dipole orientations by exciting an unstructured gold surface and a ridge nanoantenna with an in-plane dipolar plasmon resonance. The light emission is collected with an aluminum half paraboloid mirror. We show how to take the effect of the paraboloid mirror on the emission polarization into account and how to predict the polarization-filtered pattern if the emission polarization is known. Furthermore, we calculate that by introducing a slit in the beam path the polarization contrast in cathodoluminescence spectroscopy can be strongly enhanced. Finally, we reconstruct the emission polarization from the experimental data and show that from these field patterns we can infer the orientation of the induced dipole moment. The ability to measure the emission polarization, in combination with the sensitivity to the local density of optical states, broad spectral range and high excitation resolution, can be employed to study photonic nanostructures in great detail.

Studies on free energies of solution and its components of thiazole amine derivatives

The polarizable continuum model (PCM) is employed to investigate theoretically the solvation of two heterocyclic compounds containing halogens. The PCM analysis has been carried out for 4-(4-chlorophenyl)-1,3-thiazol-2-amine and 4-(4-bromophenyl)-1,3-thiazol-2-amine in ten solvents with wide range of dielectric constants. In this paper, we report the results obtained in the computation of electrostatic interaction, repulsive component of Gibb's free energy of solvation, cavitation enthalpy and entropy of solvation for the two thiazole amines in various solvents. The dipole moments of the two amine molecules are calculated theoretically by AM1, PM3, MNDO and ab initio methods. The induced dipole moments of these two thiazoles are also calculated in these solvents. The thermodynamic properties of the systems, such as free energies, electrostatic interaction, cavitation enthalpy and dipole moment are discussed in terms of the physical properties such as dielectric constant, index of refraction, surface tension and molecular size of the solvents.

Electro-optics of solutions of biopolymers and their complexes

The review summarizes the results of electric-birefringence studies of the molecular properties of biopolymers and their complexes. The application of alternating electric fields makes it possible to study the kinetics of orientation of DNA, RNA, and polypeptide molecules in diluted solutions. An analysis of molecular-mass dependences of relaxation times of biopolymer molecules in terms of the rotational friction theory is used to determine the equilibrium rigidity of macromolecules characterized by Kuhn segment length A. For DNA molecules in buffer solutions with a low ionic strength, the value of A derived from electro-optical measurements is 114 nm. The high sensitivity of electric birefringence to changes in the secondary and tertiary structures of biopolymers ensures its use for the analysis of sequence curvature in short fragments of DNA and for investigation of transitions between different tertiary structures of RNA. The study of electro-optical birefringence in solutions of complexes of DNA and polypeptides with oppositely charged ions of surfactants makes it possible to gain insight into their conformational properties in organic solvents. The stoichiometric complexes of DNA in chloroform occur in the compact globular state, whereas the conformation of complexes formed by various polypeptides depends on their composition and may vary from rodlike to coiled. Electric birefringence in solutions of biopolymer complexes is associated with the orientation of molecules that is due to the external-field-induced dipole moment that appears as a result of a small displacement of ions along the contour of polyion chains. The time of reaching the induced dipole moment is equal to or greater than the time of orientational relaxation of the complex as a whole.

Advances in Model Development for Carbon Nanotube Assembly by Dielectrophoresis

As a new type of materials, carbon nanotubes (CNTs) have been intensively studied due to their outstanding properties. Dielectrophoresis (DEP) is an effective method to assemble CNTs across a pair of electrical conductors for various applications. In DEP, CNTs suspended in dielectric liquid medium suffer a force imbalance due to induced dipole moment when subject to an externally applied non-uniform electric field, and move towards and finally deposit onto the electrode region. As a model plays a critical role in the numerical study of the DEP process, this paper introduces the theoretical background of DEP and basic DEP models based on the effective dipole moment method which has been widely accepted in the study of DEP. Particularly, the DEP force calculation methods developed recently for improved precision using these basic models are presented and discussed. A DEP model with high computing accuracy helps precisely predict a DEP process.