Static Dipole Research Articles

Mixing of isoscalar and isovector characteristics in the low-energy dipole mode

We investigated isospin splitting in low-energy dipole (LED) states of spherical nuclei such as 40Ca, 90Zr, 132Sn, 208Pb, and several N=50 isotones using self-consistent Hartree–Fock plus random phase approximation calculations. Our analysis of isovector dipole (IVD) and isoscalar dipole (ISD) strengths, along with transition densities, reveals a clear energy-dependent relationship between IS and IV modes in 40Ca and 90Zr. For 208Pb and 132Sn, LED states show mixed IS + IV characteristics due to different neutron and proton shell structures. In N=50 isotones, E1 modes exhibit varying IS and IV properties with smooth transitions as neutron excess increases. Our results suggest that compressional ISD strengths could provide valuable insights into the slope parameter of the nuclear equation of state. The observed dependence on nuclear shell structures and neutron–proton correlations highlights the need for precise measurements and further research in nuclear physics.

Interlayer excitons in MoS2/CSiH2/WS2 heterostructures: the role of the Janus intermediate layer

The introduction of intermediate hexagonal boron nitride (hBN) between the bilayer transition metal dichalcogenide (TMD) heterostructures has been considered an efficient approach to manipulate the interlayer excitations. However, the hBN intercalation primarily serves as a spacer to increase the interlayer distance and alter the screening, without producing a significant band offset shift. Here, we use Janus monolayer CSiH2, possessing a prominent out-of-plane intrinsic dipole moment and large enough band gap, as an intercalation to build trilayer MoS2/CSiH2/WS2heterostructures. Our calculated results by means of many-body perturbation theory reveal that the band alignment characteristics and the band gaps are dramatically altered in the presence of the CSiH2monolayer, due to the large potential drop across the interface of bilayer TMDs. By solving the Bethe-Salpeter equation, we observe the static dipole moment of the interlayer excitons (IXs) can be reversed through tuning the stacking sequence of CSiH2. More importantly, the radiative lifetime of IX has been substantially prolonged in MoS2/CSiH2/WS2, several orders of magnitude longer than that of bilayer MoS2/WS2, and varies between 10-9-10-5s at 0 K with different stacking sequence of CSiH2. Our explorations open the feasibility of simultaneously engineering the band alignment and the dipole moment of the dipolar IXs in TMD van der Waals heterostructures, through the introduction of Janus intercalation.

Relativistic and electron-correlation effects in static dipole polarizabilities for main-group elements

Relativistic and electron-correlation effects in static dipole polarizabilities for main-group elements

Electric dipole polarizabilities and tune-out wavelengths for 23S1 and 33S1 states of Be2.

The electric dipole polarizabilities and the tune-out wavelengths for the n3S1 (n = 2, 3) states of Be2+ are determined through the application of the relativistic full-configuration-interaction approach. Our calculations directly integrate the mass shift operator into the Dirac-Coulomb-Breit Hamiltonian and further assess the quantum electrodynamics (QED) correction to the dynamic dipole polarizabilities using perturbation theory. The results reveal that the static electric dipole polarizability of the 23S1 and 33S1 states, as well as the 93nm tune-out wavelength of the 23S1 state and the 238nm tune-out wavelength of the 33S1 state, exhibits a high sensitivity to QED correction, which exceeds 80 ppm, providing a sensitive test for atomic structure theory.

Influence of Substituents on the Vectorial Difference Static Dipole Upon Excitation in Synthetic Bacteriochlorins.

Organic dye aggregates have been shown to exhibit exciton delocalization in natural and synthetic systems. Such dye aggregates show promise in the emerging area of quantum information science (QIS). We believe that the difference in static dipole (Δd) is an essential dye parameter in the development of molecular QIS systems. However, a foundational understanding of the structural factors influencing Δd remains elusive. Bacteriochlorins play a vital role in photosynthesis due to their exceptional photophysical properties. Therefore, bacteriochlorins are particularly suitable dyes for the construction of aggregate systems for QIS. Synthetic bacteriochlorins further offer stability and tunability via chemical modifications. Here, the influence of substituents on the Δd of monomeric (nonaggregated) dyes was investigated via density functional theory (DFT) and time-dependent (TD)DFT in a set of 5-methoxybacteriochlorins progressively substituted with ethynyl, phenyl, and phenylethynyl substituents at the 3,13 and 3,13,15 positions of the macrocycle. Symmetrically substituted 5-methoxybacteriochlorins were shown to have the largest Δd. The increase in Δd in the series of dyes was largely due to changes in the orientation of the static dipole upon excitation rather than large changes in magnitude. In addition, the transition dipole (μ) and the angle between Δd and μ (ζ) were calculated. Three 5-methoxybacteriochlorins with large predicted Δd and μ values were synthesized and characterized spectroscopically. The trend in Δd values empirically determined using the solvatochromic Stokes shift method was comparable to the DFT calculations.

Dual-Vacancy-Engineered ZnIn2S4 Nanosheets for Harnessing Low-Frequency Vibration Induced Piezoelectric Polarization Coupled with Static Dipole Field to Enhance Photocatalytic H2 Evolution.

This study investigates the impact of In- and S-vacancy concentrations on the photocatalytic activity of non-centrosymmetric zinc indium sulfide (ZIS) nanosheets for the hydrogen evolution reaction (HER). A positive correlation between the concentrations of dual In and S vacancies and the photocatalytic HER rate over ZIS nanosheets is observed. The piezoelectric polarization, stimulated by low-frequency vortex vibration to ensure the well-dispersion of ZIS nanosheets in solution, plays a crucial role in enhancing photocatalytic HER over the dual-vacancy engineered ZIS nanosheets. The piezoelectric characteristic of the defective ZIS nanosheets is confirmed through the piezopotential response measured using piezoelectric force microscopy. Piezophotocatalytic H2 evolution over the ZIS nanosheets is boosted under accelerated vortex vibrations. The research explores how vacancies alter ZIS's dipole moment and piezoelectric properties, thereby increasing electric potential gradient and improving charge-separation efficiency, through multi-scale simulations, including Density Functional Theory and Finite Element Analysis, and a machine-learning interatomic potential for defect identification. Increased In and S vacancies lead to higher electric potential gradients in ZIS along [100] and [010] directions, attributing to dipole moment and the piezoelectric effect. This research provides a comprehensive exploration of vacancy engineering in ZIS nanosheets, leveraging the piezopotential and dipole field to enhance photocatalytic performances.

Beyond monopole electrostatics in regulating conformations of intrinsically disordered proteins.

Conformations and dynamics of an intrinsically disordered protein (IDP) depend on its composition of charged and uncharged amino acids, and their specific placement in the protein sequence. In general, the charge (positive or negative) on an amino acid residue in the protein is not a fixed quantity. Each of the ionizable groups can exist in an equilibrated distribution of fully ionized state (monopole) and an ion-pair (dipole) state formed between the ionizing group and its counterion from the background electrolyte solution. The dipole formation (counterion condensation) depends on the protein conformation, which in turn depends on the distribution of charges and dipoles on the molecule. Consequently, effective charges of ionizable groups in the IDP backbone may differ from their chemical charges in isolation-a phenomenon termed charge-regulation. Accounting for the inevitable dipolar interactions, that have so far been ignored, and using a self-consistent procedure, we present a theory of charge-regulation as a function of sequence, temperature, and ionic strength. The theory quantitatively agrees with both charge reduction and salt-dependent conformation data of Prothymosin-alpha and makes several testable predictions. We predict charged groups are less ionized in sequences where opposite charges are well mixed compared to sequences where they are strongly segregated. Emergence of dipolar interactions from charge-regulation allows spontaneous coexistence of two phases having different conformations and charge states, sensitively depending on the charge patterning. These findings highlight sequence dependent charge-regulation and its potential exploitation by biological regulators such as phosphorylation and mutations in controlling protein conformation and function.

Temperature tunability of topological phase transitions and edge states in two-dimensional acoustic topological insulators

Topological insulators are characterized by exhibiting an internal insulating state but a surface conductor state, which makes them advantageous for applications in novel devices. However, for most given acoustic topological metamaterials, the operating frequency is relatively fixed and the effect of temperature on their topological properties is rarely considered. Therefore, a temperature-tunable acoustic topological insulator is constructed in this paper. The quadruple degenerate Dirac cone formed at Γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Gamma$$\\end{document} point can be opened by adjusting the temperature, causing topological band inversion between the doubly degenerate dipolar and quadrupole states, and achieving topological phase transition. The evolution of its topological state with temperature is numerically investigated and a novel topological acoustic waveguide is constructed. The switching effect of temperature on the waveguide device is verified by numerical simulation and experiment. Non-contact active modulation of edge states in the structure is achieved by temperature-controlled topological phases, exhibiting acoustic switching effects. This study can provide corresponding references for the intelligent control of acoustic topology in noise, vibration, and other aspects.

Demonstration of a tunable interface between Rydberg atoms and superconducting microwave circuits with differential polarizability nulling

Microwave-dressed Rydberg atoms in pairs of states that are optically accessible and engineered so that the frequency of the transition between them is tunable while exhibiting a low sensitivity to stray electric fields have been interfaced with a superconducting coplanar waveguide (CPW) microwave resonator. This was achieved with helium atoms in triplet Rydberg states with principal quantum numbers n=55 and 56. The atoms were dressed with two strong microwave fields—a control field and a differential polarizability nulling field. The control field allowed the atoms to be coupled to the resonator using the two-color two-photon transition between the equal parity 1s55sS13≡|55s〉 and 1s56sS13≡|56s〉 Rydberg states, with one photon supplied by it and the other provided by the resonator. The nulling field was detuned from the field-free 1s55sS13→1s55pPJ3≡|55p〉 transition to admix |55p〉 character into the |55s〉 state and eliminate the differential static electric dipole polarizability of the |55s〉 and |56s〉 states. The experiments were performed with atoms located ∼300µm above a λ/4 niobium nitride superconducting CPW resonator operated at temperatures between 3.59 and 3.73K. The measured ac and dc Stark shifts of the Rydberg states at this atom-circuit interface in the presence of the dressing fields are in good quantitative agreement with the results of Floquet calculations. The differential polarizability nulling fields used in the experiments allowed the difference in the Stark shifts of the |55s〉 and |56s〉 states over the range of dc fields offset from the residual stray field by ±65 mV/cm to be reduced from 2π×2.1 MHz to 2π×125 kHz. Published by the American Physical Society 2024

Effect of dipolar state on J-type aggregation of acceptor group modified pyrene-based push-pull systems

The present work demonstrates the ground and excited state aggregation behavior of two pyrene-based push–pull systems (Pyr-MC and Pyr-PyA) both in solid and solution state. The UV–Vis spectra of these molecules show a unique broaden spectral pattern at lower energy region (400–600 nm) in both H2O and solid state. Further, along with the local (intense) emission band, a new (less intense) band is appeared at higher wavelength region (∼550 nm) in water, which is due to the formation of aggregates. Interestingly, it is the lowest energy emission out of all previously reported emission by pyrene derivatives. The experimental results suggest the formation of J-type aggregation in solid and solution. The average lifetime of these molecules is also measured in different solvents. Intriguingly, the ground/excited state J-type aggregation in solid and solution are similar in nature in spite of different mode of intermolecular interactions, and are supported by experimental results. The dipolar state plays an important role on the J-type aggregation process. The QTAIM (quantum theory of atom in molecule) theoretical framework is applied to analyze and understand the properties of molecules in terms of the distribution of electrons and the topological features of the electron density within a molecule. Importantly, bond paths provide information about the nature of chemical bonds, including their strength and directionality.

Extending the Tavis-Cummings model for molecular ensembles-Exploring the effects of dipole self-energies and static dipole moments.

Strong coupling of organic molecules to the vacuum field of a nanoscale cavity can be used to modify their chemical and physical properties. We extend the Tavis-Cummings model for molecular ensembles and show that the often neglected interaction terms arising from the static dipole moment and the dipole self-energy are essential for a correct description of the light-matter interaction in polaritonic chemistry. On the basis of a full quantum description, we simulate the excited-state dynamics and spectroscopy of MgH+ molecules resonantly coupled to an optical cavity. We show that the inclusion of static dipole moments and the dipole self-energy is necessary to obtain a consistent model. We construct an efficient two-level system approach that reproduces the main features of the real molecular system and may be used to simulate larger molecular ensembles.

Exploring charge transport dynamics in a cryogenic P-type germanium detector

This study explores the dynamics of charge transport within a cryogenic P-type Ge particle detector, fabricated from a crystal cultivated at the University of South Dakota. By subjecting the detector to cryogenic temperatures and an Am-241 source, we observe evolving charge dynamics and the emergence of cluster dipole states, leading to the impact ionization process at 40 mK. Our analysis focuses on crucial parameters: the zero-field cross-section of cluster dipole states and the binding energy of these states. For the Ge detector in our investigation, the zero-field cross-section of cluster dipole states is determined to be 8.45 × 10−11 ± 4.22 × 10−12 cm2. Examination of the binding energy associated with cluster dipole states, formed by charge trapping onto dipole states during the freeze-out process, reveals a value of 0.034 ± 0.0017 meV. These findings shed light on the intricate charge states influenced by the interplay of temperature and electric field, with potential implications for the sensitivity in detecting low-mass dark matter.

Towards modelling AR Sco: generalized particle dynamics and strong radiation-reaction regimes

ABSTRACT Numerical simulations of relativistic plasmas have become more feasible, popular, and crucial for various astrophysical sources with the availability of computational resources. The necessity for high-accuracy particle dynamics is especially highlighted in pulsar modelling due to the extreme associated electromagnetic fields and particle Lorentz factors. Including the radiation-reaction force in the particle dynamics adds even more complexity to the problem, but is crucial for such extreme astrophysical sources. We have also realized the need for such modelling concerning magnetic mirroring and particle injection models proposed for AR Sco, the first white dwarf pulsar. This paper demonstrates the benefits of using higher-order explicit numerical integrators with adaptive time-step methods to solve the full particle dynamics with radiation-reaction forces included. We show that for standard test scenarios, namely various combinations of uniform E- and B-fields and a static dipole B-field, the schemes we use are equivalent to and in extreme field cases outperform standard symplectic integrators in accuracy. We show that the higher-order schemes have massive computational time improvements due to the adaptive time-steps we implement, especially in non-uniform field scenarios and included radiation reaction where the particle gyro-radius rapidly changes. When balancing accuracy and computational time, we identified the adaptive Dormand–Prince eighth-order scheme to be ideal for our use cases. The schemes we use maintain accuracy and stability in describing the particle dynamics and we indicate how a charged particle enters radiation-reaction equilibrium and conforms to the analytical Aristotelian Electrodynamics expectations.

Cavity‐Enhanced Superfluorescence Stimulates Coherent Energy Transfer in a Perovskite Quantum Dot Superlattice

AbstractThe exploration of cooperative states in many‐body systems is a key research area. It focuses on superfluorescence (SF), a phenomenon linked with radiative dipole coupling, and its intersection with classical lasing effects. This produces a unique lasing‐field‐hybrid cooperative dipole (LCD) state through optical cavity‐enhanced superfluorescence (CESF). A coherent energy transfer is demonstrated between two such states within a perovskite quantum dot (QD) superlattice. This results in competitive luminescence timing dynamics. The findings reveal that stimulated energy transfer occurs when two cooperative cavity‐exciton states coexist, controllable via a dual‐pulse pump technique. This understanding is vital for advancing quantum phenomena knowledge and enhancing optoelectronic devices.

Dynamic and static dipole polarizability of an Aharonov–Bohm ring

The properties of nanoscale rings are sensitive to Aharonov–Bohm fluxes threading the ring. In particular, neighboring angular momentum eigenstates become degenerate in cases of half-integer flux. Such degeneracies have a profound effect on the dipole polarizability leading to a divergent response. We analyze circular finite-width nanorings and derive a simple and compact expression for the polarizability valid for arbitrary ring geometry, frequency and magnetic flux. The dipole response is significantly reduced by finite-width effects, yet divergencies at half-integer flux are predicted irrespective of width. Finally, a non-divergent (but large) response is restored through a non-perturbative treatment of both magnetic and electric fields.

Evaluating aliphatic CF, CF2, and CF3 groups as vibrational Stark effect reporters.

Given the extensive use of fluorination in molecular design, it is imperative to understand the solvation properties of fluorinated compounds and the impact of the C-F bond on electrostatic interactions. Vibrational spectroscopy can provide direct insights into these interactions by using the C-F bond stretching [v(C-F)] as an electric field probe through the vibrational Stark effect (VSE). In this work, we explore the VSE of the three basic patterns of aliphatic fluorination, i.e., mono-, di-, and trifluorination in CF, CF2, and CF3 groups, respectively, and compare their response to the well-studied aromatic v(C-F). Magnitudes (i.e., Stark tuning rates) and orientations of the difference dipole vectors of the v(C-F)-containing normal modes were determined using density functional theory and a molecular dynamics (MD)-assisted solvatochromic analysis of model compounds in solvents of varying polarity. We obtain Stark tuning rates of 0.2-0.8cm-1/(MV/cm), with smallest and largest electric field sensitivities for CFaliphatic and CF3,aliphatic, respectively. While average electric fields of solvation were oriented along the main symmetry axis of the CFn, and thus along its static dipole, the Stark tuning rate vectors were tilted by up to 87° potentially enabling to map electrostatics in multiple dimensions. We discuss the influence of conformational heterogeneity on spectral shifts and point out the importance of multipolar and/or polarizable MD force fields to describe the electrostatics of fluorinated molecules. The implications of this work are of direct relevance for studies of fluorinated molecules as found in pharmaceuticals, fluorinated peptides, and proteins.

All-electron basis sets for H to Xe specific for ZORA calculations: Applications in atoms and molecules

Abstract A segmented basis set of quadruple zeta valence quality plus polarization functions (QZP) for H through Xe was developed to be used in conjunction with the ZORA Hamiltonian. This set was augmented with diffuse functions to describe electrons farther away from the nuclei adequately. Using the ZORA-CCSD(T)/QZP-ZORA theoretical model, atomic ionization energies and bond lengths, harmonic vibrational frequencies, and atomization energies of some molecules were calculated. The addition of core-valence corrections has been shown to improve the agreement between theoretical and experimental results for molecular properties. For atomization energies, a similar observation emerges when considering spin-orbit couplings. With the augmented QZP-ZORA set, static mean dipole polarizabilities of a set of atoms were calculated and compared with previously published recommended and experimental values. Performance evaluations of the ZORA and Douglas–Kroll–Hess Hamiltonians were made for each property studied.

Spatially resolved work-function manipulation of azobenzene-functionalized self-assembled monolayers by optical stimulation

Strongly differing static dipole moments of the trans and cis isomers of photochromic azobenzene allow for optical switching of the work function of azobenzene-functionalized self-assembled monolayers (SAMs). We apply these properties in a fundamental experiment to manipulate the area size of the switched SAM. Azobenzene molecules were excited by ultraviolet laser illumination, and the transient isomerization profile of the SAM was spatially resolved recording photoemission electron microscopy images. Thereby, we demonstrate the spatial tuning of the SAM's work function and discuss the role of the laser spot profile in generating sharp edges or gradual changes of the work function.

P-Phenylene bridge induced dual twisting and metameric impacts on molecular structure and dipole Moments: A computational study on pyridinium phenolate mesomeric betaines using linear response theory

In this contribution, molecular structures, and dipole moments (using self-consistent and linear response theories) were reported for two p-phenylene bridged mesomeric betaines, using AM1, HF, B3LYP, B3PW91, M06-2X, LC-ωPBE, CAM-B3LYP, MP2 and CASSCF methodologies. In this work (1) metameric influences on molecular conformations, and (2) molecular electric dipole moments, and then (3) impact of bridge by comparing with unbridged derivatives, are investigated. Metameric influence on conformational preference was observed and p-phenylene bridge was found to be acting like a facilitator. While most of the methodologies predicted only reasonable impacts of metamerism on molecular dipole moments; the CASSCF method predicted around 2-fold enhanced dipole moment for Reichardt’s type than Brooker’s type. p-phenylene bridge effectively enhanced the dipole moments (∼2-fold) than non-bridged zwitterions. Linear response theory-based (field-dependent) results were found to be similar to the static (field-independent) dipole moments. HF, MP2 and CASSCF exhibited similar behaviors, and DFT-based methodologies very different characteristics.

Bound state energies and critical bound region in the semiclassical dense hydrogen plasmas

We calculate the bound state energies of the hydrogen atom in semiclassical dense hydrogen plasmas modeled by the effective screened interaction potential developed by Ramazanov et al. [Phys. Rev. E 92, 023104 (2015)]. It is shown that the quantum degenerate and exchange-correlation effects of plasma electrons do not play significant roles in the region where the system exhibits bound states. The bound-continuum critical transition lines and the distribution of the ground state energies in the plasma density-temperature phase diagrams are obtained, both with and without taking into account the screening effect of the plasma ions. The dipole transition oscillator strengths and static dipole polarizabilities of the electron-ion subsystems in semiclassical dense hydrogen plasmas are calculated in a wide range of plasma parameters.