Atomic Polarizabilities Research Articles

Compensation of Hybridization Defects in Phosphorescent Complexes with Pnictogen-Based Ligands-A Structural, Photophysical, and Theoretical Case-Study with Predictive Character.

In this work, for the first time, the comparative use of P-, As-, and Sb-based ligands in phosphorescent coordination compounds is reported toward new coordination chemical concepts in the design and realization of tailored triplet emitters with nonconventional elements. By means of spectroscopic, X-ray diffractometric, and quantum-chemical methods, we reconstructed the nature of the chemical bonds as well as the influence of the increasingly heavy elements on the photoexcited state properties, which were correlated with the hybridization and polarizability of the pnictogen atoms (Pn). In particular, we elucidated the structural and photophysical properties of a series of homologous Pt(II) complexes with monodentate ancillary ligands based on group 15 elements, namely P, As, and Sb. Six coordination compounds bearing tridentate dianionic 2,6-bis(1H-1,2,4-triazol-5-yl)pyridine luminophoric pincer ligands bearing either CF3 or tBu moieties on the triazole rings along with triphenylpnictogens (PnPh3) as monodentate ancillary ligands ([CF3/Pn] or [tBu/Pn], respectively) have been investigated. The electron donating or withdrawing effect of the peripheral substituent (tBu vs. CF3, respectively) and its influence on the bonding, crystal packing as well as the excited state energies and lifetimes was assessed in fluid solutions, frozen glassy matrices, amorphous solids, and crystalline phases. A progressively red-shifted phosphorescence was observed with increasing atomic number along with a growing compensation of hybridization defects upon coordination of the Pn atom to the Pt(II) center. The change of molecular geometry of the PnPh3 unit upon complexation was extrapolated to predict the structural and excited state characteristics of the Bi-based analogues, which according to DFT calculations should be stable species and are the subject of ongoing synthetic efforts. In general, we envisage the use of these ligands for the relativistic enhancement of radiative deactivation rate processes, especially if Bi-based s-orbitals participate on the bond with the metal center, paving the road toward novel coordination compounds using abundant elements with high spin-orbit coupling for sustainable electroluminescent devices.

Random Matrix Theory Analysis of a Temperature-Related Transformation in Statistics of Fano-Feshbach Resonances in Thulium Atoms.

Recently, the transformation from random to chaotic behavior in the statistics of Fano–Feshbach resonances was observed in thulium atoms with rising ensemble temperature. We performed random matrix theory simulations of such spectra and analyzed the resulting statistics in an attempt to understand the mechanism of the transformation. Our simulations show that, when evaluated in terms of the Brody parameter, resonance statistics do not change or change insignificantly when higher temperature resonances are appended to the statistics. In the experiments evaluated, temperature was changed simultaneously with optical dipole trap depth. Thus, simulations included the Stark shift based on the known polarizability of the free atoms and assuming their polarizability remains the same in the bound state. Somewhat surprisingly, we found that, while including the Stark shift does lead to minor statistical changes, it does not change the resonance statistics and, therefore, is not responsible for the experimentally observed statistic transformation. This observation suggests that either our assumption regarding the polarizability of Feshbach molecules is poor or that an additional mechanism changes the statistics and leads to more chaotic statistical behavior.

Dynamic Multipole Polarizabilities of Helium and Screened-Helium Atoms

The precise estimation of atomic polarizabilities impinges upon a number of areas and processes in physical science. We calculate precisely the dynamic multipole polarizabilities of the helium and screened-helium atoms using highly correlated exponential wavefunctions based on the pseudo-state summation method. For screened environments, we consider the Debye–Hückel potential (DHP) as the interaction potentials between the charged particles. The dynamic multipole (quadrupole, octupole, and hexadecapole) polarizabilities for the ground state of the helium atom and the multipole (quadrupole and octupole) polarizabilities of the screened-helium atom for different screening parameters are reported along with magic-zero wavelengths. The reported results for hexadecapole polarizability of the helium atom and dynamic multipole polarizability of the screened-helium atom are new and would be useful for future investigation on this topic.

Precision protection through cosmic string in quantum metrology

The dynamics of the quantum Fisher information of the parameters of the initial atomic state and atomic transition frequency is studied, in the framework of open quantum systems, for a static polarizable two-level atom coupled in the multipolar scheme to a bath of fluctuating vacuum electromagnetic fields in cosmic string space-time. Our results show that with the presence of cosmic string, the quantum Fisher information becomes position and atomic polarization dependent. It may be enhanced or depressed as compared to that in flat space-time case. Remarkably, when the atom is extremely close to the cosmic string and the polarization direction of the atom is perpendicular to the direction of the cosmic string, the quantum Fisher information has been totally protected from the fluctuating vacuum electromagnetic fields. So on the one hand, near a cosmic string, precision of estimation can be enhanced by ranging the radial distance between the probe atom and the cosmic string; on the other hand, the cosmic string can be sensed by studying the distribution of parameter induced state-separation.

Calculation of Polarizabilities for Atoms with Open Shells

A version of the configuration interaction method for atoms with open shells (the Configuration Interaction with Perturbation Theory—CIPT method, PRA 95, 012503 (2017)) is extended for calculation of static and dynamic polarizabilities. Its use is demonstrated by calculation of the polarizabilities for the ground and excited states of Er, Tm and Yb. It is proved to be an useful tool in designing a new generation of optical atomic clocks sensitive to new physics.

Crystal Field Effects on Atomic and Functional-Group Distributed Polarizabilities of Molecular Materials.

To rationally design new molecular materials with desirable linear optical properties, such as refractive index or birefringence, we investigated how atomic and functional-group polarizability tensors of prototypical molecules respond to crystal field effects. By building finite aggregates of urea, succinic acid, p-nitroaniline, 4-mercaptopyridine, or methylbenzoate, and by partitioning the cluster electronic density using quantum theory of atoms in molecules, we could extract atoms and functional groups from the aggregates and estimate their polarizability enhancements with respect to values calculated for molecules in isolation. The isotropic polarizability and its anisotropy for the molecular building blocks are used to understand the functional-group sources of optical properties in these model systems, which could help the synthetic chemist to fabricate efficient materials. This analysis is complemented by benchmarking density functionals for atomic distributed polarizabilities in gas phase, by comparing the results with refractive-index calculations under periodic boundary conditions, and by estimating functional-group optical properties from a classical electrostatic atom-dipole interaction model.

Theoretical determination of polarizability and magnetic susceptibility of neon

We report theoretical determination of the dipole polarizability of the neon atom, including its frequency dependence. Corrections for the relativistic, quantum electrodynamics, finite nuclear mass, and finite nuclear size effects are taken into account. We obtain the value $\alpha_0=2.66080(36)$ for the static polarizability, and $\alpha_2=2.850(7)$ and $\alpha_4=4.932(14)$ for the first two polarizability dispersion coefficients (Cauchy moments); all values are in atomic units (a.u.). In the case of static polarizability, our result agrees with the best experimental determination [C. Gaiser and B. Fellmuth, Phys. Rev. Lett. 120, 123203 (2018)], but our estimated uncertainty is significantly larger. For the dispersion coefficients, the results obtained in this work appear to be the most accurate to date overall compared to published theoretical and experimental data. We also calculated the static magnetic susceptibility of the neon atom, needed to obtain the refractive index of gaseous neon. Our result, $\chi_0 = -8.484(19) \cdot 10^{-5}$ a.u., is about 9% larger in absolute value than the recommended experimental value [CRC Handbook of Chemistry and Physics, CRC Press, 2019, p. 4-145].

Magic Wavelengths for Optical-Lattice Based Cs and Rb Active Clocks

Active clocks could provide better stabilities during initial stages of measurements over passive clocks, in which stabilities become saturated only after long-term measurements. This unique feature of an active clock has led to search for suitable candidates to construct such clocks. The other challenging task of an atomic clock is to reduce its possible systematics. A major part of the optical lattice atomic clocks based on neutral atoms are reduced by trapping atoms at the magic wavelengths of the optical lattice lasers. Keeping this in mind, we find the magic wavelengths between all possible hyperfine levels of the transitions in Rb and Cs atoms that were earlier considered to be suitable for making optical active clocks. To validate the results, we give the static dipole polarizabilities of Rb and Cs atoms using the electric dipole transition amplitudes that are used to evaluate the dynamic dipole polarizabilities and compare them with the available literature values.

Polarizabilities of neutral atoms and atomic ions with a noble gas electron configuration.

Atomic polarizabilities play an important role in the development of force fields for molecular simulations, as well as for the development of qualitative concepts of atomic and molecular behavior. Coupled cluster theory at the coupled cluster singles doubles triples level with very large correlation-consistent basis sets with extended diffuse functions has been used to predict the polarizabilities of the atomic neutrals, mono-cations and mono-anions with a noble gas configuration. Additional corrections for scalar relativistic and spin-orbit effects were also included for the electron configurations of Kr, Xe, and Rn. The results are in excellent agreement with experiment or with other high level calculations where available. The current results for most of these species represent the best available values for the polarizabilities. The results show that the polarizability of H- is very difficult to calculate without extremely diffuse functions. The polarizability of H- is the largest value, 34.05 Å3, calculated for all species in the current study. The polarizabilities of the remaining halogen anions are also the best available values. The polarizabilities of the halogen anions (excluding F-) and H- have a linear correlation with the electron affinity of the neutral atom. Spin-orbit effects, even for closed shell species, cannot be ignored for quantitative accuracy, and the inclusion of spin-orbit effects for Fr+, Rn, and At- increases the polarizability by 4%, 6%, and 15%, respectively.

Effect of Bi addition on optical properties of Se–Te–Bi films

The present paper reports the optical properties of Se80−xTe20Bix (0 ≤ x ≤ 12) films. Melt quenching method has been employed to prepare amorphous bulk samples, and thermal evaporation method has been used to deposit films of the samples under the vacuum of 10−5 torr. The structural characterization of films was carried out using X-ray diffraction and transmission electron microscopy. The X-ray diffraction studies showed that samples are amorphous in nature, while surface morphology results indicated the formation of nanorods of diameter 20–100 nm. The absorption and transmission spectra were recorded in the wavelength range 400–2500 nm, and data were used to determine refractive index, thickness of film, extinction coefficient and band gap of film samples. It was found that refractive index increases from 1.76 to 1.94 on increase in Bi wt% in the samples. Extinction coefficient also shows the same trend. This is due to increased polarizability of the larger Bi atoms. Further, the results show that energy band gap decreases on increase in Bi concentration in Se–Te–Bi nanostructured system. The value of Eg for x = 0 is 1.43 eV, while for x = 12, it decreases to 0.27 eV. The decrease in band gap is due to increase in the number of localized states, which eventually narrows the optical band gap. The values of band tail width (Ee) were also found to increase from 0.064 to 0.460 on Bi addition to Se–Te system. The small value of band gap and extinction coefficient makes these nanostructured films suitable for nano-electronic devices and anti-reflection multi layers.

Benchmarking polarizable and non-polarizable force fields for Ca2+-peptides against a comprehensive QM dataset.

Explicit description of atomic polarizability is critical for the accurate treatment of inter-molecular interactions by force fields (FFs) in molecular dynamics (MD) simulations aiming to investigate complex electrostatic environments such as metal-binding sites of metalloproteins. Several models exist to describe key monovalent and divalent cations interacting with proteins. Many of these models have been developed from ion-amino-acid interactions and/or aqueous-phase data on cation solvation. The transferability of these models to cation-protein interactions remains uncertain. Herein, we assess the accuracy of existing FFs by their abilities to reproduce hierarchies of thousands of Ca2+-dipeptide interaction energies based on density-functional theory calculations. We find that the Drude polarizable FF, prior to any parameterization, better approximates the QM interaction energies than any of the non-polarizable FFs. Nevertheless, it required improvement in order to address polarization catastrophes where, at short Ca2+-carboxylate distances, the Drude particle of oxygen overlaps with the divalent cation. To ameliorate this, we identified those conformational properties that produced the poorest prediction of interaction energies to reduce the parameter space for optimization. We then optimized the selected cation-peptide parameters using Boltzmann-weighted fitting and evaluated the resulting parameters in MD simulations of the N-lobe of calmodulin. We also parameterized and evaluated the CTPOL FF, which incorporates charge-transfer and polarization effects in additive FFs. This work shows how QM-driven parameter development, followed by testing in condensed-phase simulations, may yield FFs that can accurately capture the structure and dynamics of ion-protein interactions.

Sideband ground-state cooling of graphene with Rydberg atoms via vacuum forces

We present a scheme leading to ground-state cooling of the fundamental out-of-plane (flexural) mode of a suspended graphene sheet. Our proposal exploits the coupling between a driven Rydberg atom and the graphene resonator, which is enabled by vacuum forces. Thanks to the large atomic polarizability of the Rydberg states, the Casimir-Polder force is several orders of magnitude larger than the corresponding force achieved for atoms in the ground state. By playing with the distance between the atom and the graphene membrane, we show that resolved sideband cooling is possible, bringing the occupation number of the fundamental flexural mode down to its quantum limit. Our findings are expected to motivate physical applications of graphene at extremely low temperatures.

Physical properties of titanates, semiconductors and nickelates derived from ionization energy theory

Ionization energy theory is exploited to predict the changes to atomic polarizability for both anions and cations, the polarization in doped titanates and the energy gap in III–V and II–VI semiconductors. We then extend the above analysis to discuss the physics of metallic and superconducting phases in the recently discovered superconducting nickelates. In doing so, we are able to prove the existence of Ni2+ cations and oxygen vacancy in the metallic normal state of nickelates. We find that the normal state resistivity of the nickelates follows exactly as predicted by the ionization energy theory. Quantitative estimates are also given for the concentrations of Ni2+ and oxygen vacancy in superconducting nickelates.

Atomic and ionic polarizabilities of B, C, N, O, and F

AbstractAccurate polarizabilities of atoms and molecules are critical in the treatment of optical and dielectric properties, in the modeling and interpretation of intermolecular interactions, in scattering processes, and in chemical reactivity. In this work we provide a systematic study of the atomic/ionic static dipole polarizabilities of the first‐row elements: B+, B, B−, C2+, C+, C, C−, N2+, N+, N, O2+, O+, O, O−, F2+, F+, F, and F−. We used the CCSD(T) method with a range of large correlation‐consistent basis sets augmented with a series of diffusion functions (x‐aug‐cc‐pVXZ). We discuss the trends in the dependence of dipole polarizability from the basis set size and/or number of diffuse functions and report the recommended values of average dipole polarizabilities for this series. The systematic survey of dipole polarizabilities for ions from boron to fluorine, including the extrapolation to complete basis set limit, is presented for the first time.

Casimir and Casimir-Polder Forces in Graphene Systems: Quantum Field Theoretical Description and Thermodynamics

We review recent results on the low-temperature behaviors of the Casimir-Polder and Casimir free energy an entropy for a polarizable atom interacting with a graphene sheet and for two graphene sheets, respectively. These results are discussed in the wide context of problems arising in the Lifshitz theory of van der Waals and Casimir forces when it is applied to metallic and dielectric bodies. After a brief treatment of different approaches to theoretical description of the electromagnetic response of graphene, we concentrate on the derivation of response function in the framework of thermal quantum field theory in the Matsubara formulation using the polarization tensor in (2 + 1)-dimensional space—time. The asymptotic expressions for the Casimir-Polder and Casimir free energy and entropy at low temperature, obtained with the polarization tensor, are presented for a pristine graphene as well as for graphene sheets possessing some nonzero energy gap Δ and chemical potential μ under different relationships between the values of Δ and μ. Along with reviewing the results obtained in the literature, we present some new findings concerning the case μ≠0, Δ=0. The conclusion is made that the Lifshitz theory of the Casimir and Casimir-Polder forces in graphene systems using the quantum field theoretical description of a pristine graphene, as well as real graphene sheets with Δ>2μ or Δ<2μ, is consistent with the requirements of thermodynamics. The case of graphene with Δ=2μ≠0 leads to an entropic anomaly, but is argued to be physically unrealistic. The way to a resolution of thermodynamic problems in the Lifshitz theory based on the results obtained for graphene is discussed.

Dynamical Casimir effect in resonance fluorescence

When a two-level atom interacts resonantly with a coherent electromagnetic field, the polarizability of the atom can be modulated due to the Rabi oscillations between atomic levels. We show that in the quantum vacuum, such a time-dependent atomic polarizability can lead to a resonant generation of photon pairs, a phenomenon reminiscent of photon emission in the dynamical Casimir effect (DCE). Specifically, we employ a dressing transformation to obtain an effective Hamiltonian which uncovers a polarizability-dependent parametric interaction corresponding to DCE. We determine the photon emission rate and indicate features of DCE photon pairs distinguishable from regular fluorescence photons.

The Hidden Ramsauer-Townsend Effect in Positron Scattering by Rare Gas Atoms

The aim of this work is to present and discuss the Ramsauer-Townsend effect in the context of low-energy positron scattering by rare gas atoms. Opposed to what happens in electron-atom scattering, the competition between the static repulsive and polarization attractive potentials makes the phenomenon improbable in positron case. Nonetheless, we show using a semiempirical potential formulation that, while the effect is explicitly observed in the total cross sections for He and Ne, for the heavier noble gases it becomes “hidden” or implicit. We show that as the atomic polarizability increases, the suppression of s-wave goes to higher energies due to the variation of the scattering length with the polarizability. No specific signature for the effect is found in the shape of the differential cross sections but curiously, while the effect is implicit in the total cross section for Ar, it generates a minimum structure in the momentum transfer cross section. The theme is presented for non-specialist audience with emphasis in basic atomic and scattering theories along with practical results, the main objective being to boost the traditional discussions with a new view on the subject.

Van der Waals coefficients of the multi-layered MoS2 with alkali metals

The van der Waals coefficients and the separation dependent retardation functions of the interactions between the atomically thin films of the multi-layered transition metal molybdenum disulfide (MoS2) dichalcogenides with the alkali atoms are investigated. First, we determine the frequency-dependent dielectric permittivity and intrinsic carrier density values for different layers of MoS2 by adopting various fitting models to the recently measured optical data reported by Yu and co-workers (2015 Sci. Rep. 5, 16 996) using spectroscopy ellipsometry. Then, dynamic electric dipole polarizabilities of the alkali atoms are evaluated very accurately by employing the relativistic coupled-cluster theory. We also demonstrate the explicit change in the above coefficients for different number of layers. These studies are highly useful for the optoelectronics, sensing and storage applications using layered MoS2.

Signature of Short-Range van der Waals Forces Observed in Poisson Spot Diffraction with Indium Atoms.

The phase of de Broglie matter waves is a sensitive probe for small forces. In particular, the attractive van der Waals force experienced by polarizable atoms in the close vicinity of neutral surfaces is of importance in nanoscale systems. It results in a phase shift that can be observed in matter-wave diffraction experiments. Here, we observe Poisson spot diffraction of indium atoms at submillimeter distances behind spherical submicron silicon dioxide particles to probe the dispersion forces between atoms and the particle surfaces. We compare the measured relative intensity of Poisson's spot to theoretical results derived from first principles in an earlier communication and find a clear signature of the atom-surface interaction.

Alkali-cation-incorporated and functionalized iron oxide nanoparticles for methyl blue removal/decomposition

Enhancing the rate of decomposition or removal of organic dye by designing novel nanostructures is a subject of intensive research aimed at improving waste-water treatment in the textile and pharmaceutical industries. Despite radical progress in this challenging area using iron-based nanostructures, enhancing stability and dye adsorption performance is highly desirable. In the present manuscript alkali cations are incorporated into iron oxide nanoparticles (IONPs) to tailor their structural and magnetic properties and to magnify methyl blue (MB) removal/decomposition capability. The process automatically functionalizes the IONPs without any additional steps. The plausible mechanisms proposed for IONPs incubated in alkali chloride and hydroxide solutions are based on structural investigation and correlated with the removal/adsorption capabilities. The MB adsorption kinetics of the incubated IONPs is elucidated by the pseudo second-order reaction model. Not only are the functional groups of –OH and –Cl attached to the surface of the NPs, the present investigation also reveals that the presence of alkali cations significantly influences the MB adsorption kinetics and correlates with the cation content and atomic polarizability.