Oscillator Strengths Research Articles

A holistic understanding of optical properties in amorphous H-terminated Si-nanostructures: Combining TD-DFT with AIMD

Silicon, traditionally known as an indirect band gap semiconductor, unveils intriguing properties at the nanoscale, stemming from deviations from k-conservation rules within nanostructures. In our study, we scrutinized four hydrogenated Si 0D-nanostructures—Si10H16, Si14H20, Si18H24, and Si22H28—to unravel their dynamic stability under thermal fluctuations and optical characteristics. We initiated our exploration by employing the TD-DFT framework to generate and analyze the optical properties of these geometrically optimized nanostructures. Simultaneously, we conducted ab initio molecular dynamics simulations to examine the structural robustness and thermal stability of the four structures. Leveraging the Car-Parrinello molecular dynamics approach within the Quantum ESPRESSO open software suite, we observed temperature evolution and stability differences among the nanostructures at targeted temperatures 40 and 300 K. Our subsequent investigation delved into the Turbo-Lanczos time-dependent DFT method, unraveling the optical properties and excited-state dynamics of hydrogenated Si nanostructures. The results unveiled shifts towards higher energy absorption edges E0, accompanied by alterations in the permittivity tensor, complex refractive index, oscillator strength, and reflectivity. Notably, the analysis revealed an enlarged HOMO-LUMO gap, distinctive from bulk Si. Furthermore, our models predicted the elimination of phase-dependent E1/E2 optical transition peaks in the imaginary part of the dielectric function, and a gradual decrease in the low-frequency dielectric response with increased hydrogenation of the amorphous structures. These findings underscore the promising applications of hydrogenating Si nanostructures in diverse technological domains such as optoelectronics, memristors, sensors, and quantum computing. Their tunable optical properties, size-dependent behaviors, and compatibility with existing silicon-based devices make them particularly appealing for next-generation technologies.

Electronic structure, oscillator strength, and rovibrationally resolved photodissociation of 24MgH

Aims. A series of high-precision calculations for the electronic structure of MgH have been reported in the past two decades; however, most of them d not include the core-valence correlation and still exhibit distinct differences. Furthermore, the latest high-precision results have not been applied to the studies of photodissociation dynamics. The primary motivations of this paper are to calculate a more precise electronic structure of MgH consering a core-valence correlation and to prove the photodissociation cross-sections. Methods. The electronic structure of MgH is investigated by multi-reference configuration interaction calculations with Davson correction (MRCI+Q). We performed two different sets of calculations to investigate the core-valence correlation and, as a result, obtained accurate potential energy curves (PECs) and transition dipole moments (TDMs). An extrapolation procedure was also employed to eliminate the error of basis set. Then, the photodissociation cross-sections were calculated using high-precision PECs and TDMs. Results. The PECs and TDMs of the five lowest doublet electronic states, X2Σ+, B′2Σ+, E2Σ+, A2Π, and C2Π, are obtained from calculations including core-valence correlation, termed as CV-MRCI, while PECs of the ten lowest doublet states and three quartet states are also obtained from NCV-MRCI calculations without core-valence correlation. The spectroscopic constants and band oscillator strengths are also proved with high precision levels. The equilibrium Re and vertical excitation energy Te are only 0.1% different from the measurements. Based on the CV-MRCI results, the rovibrationally resolved photodissociation cross-sections for transitions from X2Σ+ to the other four states, as well as the total local thermodynamic equilibrium cross-sections for temperatures up to 10000 K, are calculated.

ENHANCING BIOAVAILABILITY OF RESVERATROL THROUGH COMPLEXATION WITH π-ACCEPTORS: A SPECTROSCOPIC INVESTIGATION

Polyphenols, including the highly effective resveratrol, have garnered attention due to their potential as drug candidates for COVID-19 prevention and treatment, as well as their diverse biological activities. However, clinical application is hindered by limited bioavailability. To address this, complexation of resveratrol (RES) with electron-accepting compounds, such as TCNE and DDQ, was investigated. A spectroscopic and thermodynamic study of these charge transfer complexes was conducted in methanol and ethanol using UV-visible spectrophotometry. The composition of the charge transfer complexes (CTC) were determined using molar ratio method and Job's continuous variation method. Benesi-Hildbrand equation was used to calculate the formation constants KCT and the molar extinction coefficient ɛCT of the formed complexes. Thermodynamic parameters (∆G°), (∆H°), (∆S°) and other physical factors, transition energy (ECT), ionization potential (IP), resonance energy (RN), oscillator strength (ƒ) and dipole moment (μ) were determined too.Solid CTC were characterized by FT-IR and NMR spectroscopy. CTC formed in the reaction of resveratrol with both π -acceptors have high formation constants KCT indicating the high stability of these complexes. The solvent nature was identified as a factor influencing KCT values. Specifically, the KCT values for [RES-DDQ] CTC formed in ethanol surpassed those of the same complex formed in methanol. Conversely, the KCT values of [RES-TCNE] CTC formed in methanol were higher than those of the same complex formed in ethanol.This research offers insights into enhancing the properties of resveratrol through charge transfer complex formation, paving the way for potential applications in anticancer therapeutics.

On a Spectral Method for β-particle Bound Excitation Collisions in Kilonovae

The interaction of β-particles with the weakly ionized plasma background is an important mechanism for powering the kilonova (KN) transient signal from neutron star mergers. For this purpose, we present an implementation of the approximate fast-particle collision kernel, described by Inokuti following the seminal formulation of Bethe, in a spectral solver of the Vlasov–Maxwell–Boltzmann equation. In particular, we expand the fast-particle plane-wave atomic excitation kernel into coefficients of the Hermite basis, and derive the relevant discrete spectral system. In this fast-particle limit, the approach permits the direct use of atomic data, including optical oscillator strengths, normally applied to photon–matter interaction. The resulting spectral matrix is implemented in the MASS-APP spectral solver framework, in a way that avoids full matrix storage per spatial zone. We numerically verify aspects of the matrix construction, and present a proof-of-principle 3D simulation of a 2D axisymmetric KN ejecta snapshot. Our preliminary numerical results indicate that a reasonable choice of Hermite basis parameters for β-particles in the KN is a bulk velocity parameter u = 0, a thermal velocity parameter α = 0.5c, and a 9 × 9 × 9 mode velocity basis set (Hermite orders of 0–8 in each dimension). For interior-ejecta sample zones, we estimate that the ratio of thermalization from large-angle (≳2.°5) bound excitation scattering to total thermalization is ∼0.002–0.003.

A theoretical study on the solvent effects on adsorption behavior of naproxen with PLGA nanoparticles

The objective of this research is to study the influence of naproxen (NPX) adsorption on structural, electronic, and optical features of poly (lactic-co-glycolic acid) (PLGA) in the dichloromethane (CH2Cl2), chloroform (CHCl3), and water (H2O) phases through density functional dispersion correction (DFT-D) calculations. The analyses conducted in the chloroform phase, considering binding energy and chemical reactivity parameters, indicate that NPX forms stronger hydrogen bonds with PLGA in state B (−0.60 eV) compared to states A (−0.37 eV) and C (−0.47 eV), primarily through its carboxyl (–COOH) group by using B3LYP-D/6–311 + G** level of theory. The formation of hydrogen bonds between naproxen and PLGA in the chloroform phase is most stable compared to the dichloromethane and water phases. According to time-dependent density functional theory (TDDFT) calculations, the B3LYP method predicts the maximum optical absorption in the UV region for complex B, with an optical energy of 5.41 eV and an oscillator strength of 0.781, resulting in a maximum absorption peak at 229 nm. Based on the infrared (IR) spectra analysis, we find alterations in pristine PLGA and NPX due to their interaction. The interaction between NPX and PLGA results in more negative Gibbs free energy (ΔG) values, which in turn lead to an elevation in dipole moment, enhanced solubility, and a decrease in the energy gap (Eg). As a result of NPX adsorption, the decreased energy gaps enhance the electronic and optical sensitivity of PLGA to the NPX molecule.

Fluctuations in the Photoluminescence Excitation Spectra of Individual Semiconductor Nanocrystals.

Most single quantum emitters display non-steady emission properties. Models that explain this effect have primarily relied on photoluminescence measurements that reveal variations in intensity, wavelength, and excited-state lifetime. While photoluminescence excitation spectroscopy could provide complementary information, existing experimental methods cannot collect spectra before individual emitters change in intensity (blink) or wavelength (spectrally diffuse). Here, we present an experimental approach that circumvents such issues, allowing the collection of excitation spectra from individual emitters. Using rapid modulation of the excitation wavelength, we collect and classify excitation spectra from individual CdSe/CdS/ZnS core/shell/shell quantum dots. The spectra, along with simultaneous time-correlated single-photon counting, reveal two separate emission-reduction mechanisms caused by charging and trapping, respectively. During bright emission periods, we also observe a correlation between emission red-shifts and the increased oscillator strength of higher excited states. Quantum-mechanical modeling indicates that diffusion of charges in the vicinity of an emitter polarizes the exciton and transfers the oscillator strength to higher-energy transitions.

Multireference Correlated Oscillator Strengths from Adiabatic Connection Approaches Based on Extended Random Phase Approximation.

We show that accurate oscillator strengths can be obtained from adiabatic connection (AC) approaches based on the extended random phase approximation (ERPA) combined with multireference (complete active space, CAS) wave functions. The oscillator strengths calculated using the perturbation-corrected ERPA transition density matrices, proposed in this work, and the excitation energies calculated with recently introduced AC correlation energy methods, AC0 and AC0D, compete with accuracy in the perturbational CASPT2 approach and require less computational effort. AC0 and AC0D methods scale more favorably with the number of active orbitals than multiconfigurational perturbation approaches like CASPT2 and NEVPT2 thanks to their dependence on reduced density matrices up to the order of 2. Importantly, the newly developed approach for computing correlated transition dipole moments does not entail any additional costs, as all intermediate quantities become available when AC0 energies are being computed. We also test the performance of the recently proposed AC method corrected for the negative-transition contributions to the correlation energy, AC0D, for triplet excitation energies. Similarly, as for the singlet excitations, the correction improves the performance of the AC0 method, particularly for the low-lying excited states.

Generalized Transition Moment and Oscillator Strength for Optimal Control of Excited States Using Near-Field Light.

The near field is a highly localized light field that is present in the vicinity of materials. It holds considerable potential for manipulating molecular excitation through the design of nanostructures. To that end, a simple yet applicable computational method is required. This letter presents an optimization strategy to achieve targeted electronic excitation in molecules using near-field light. The generalized transition moment and oscillator strength based on the multipolar Hamiltonian can incorporate key parameters affecting the near field, including shape, size, and material composition. This calculation helps optimize electronic transitions through manipulation of the aforementioned parameters. The feasibility of the proposed scheme was demonstrated using a scanning tunneling microscopic setup with light, wherein the near field is controlled by varying the tip position in two dimensions. This approach paves the way for further innovations, which may ultimately enable precise control of molecular behavior by using tailored near-field interactions.

PyExoCross: a Python program for generating spectra and cross sections from molecular line lists

Abstract PyExoCross is a Python adaptation of the ExoCross Fortran application (Yurchenko, A&A, 614, A131 (2018)). PyExoCross is designed for postprocessing the huge molecular line lists generated by the ExoMol project and other similar initiatives such as the HITRAN and HITEMP databases. PyExoCross generates absorption and emission stick spectra, cross sections and other properties (partition functions, specific heats, cooling functions, lifetimes and oscillator strengths) based on molecular line lists. PyExoCross calculates cross sections with four line profiles: Doppler, Gaussian, Lorentzian and Voigt profiles in both sampling and binned methods; a number of options are available for computing Voigt profiles which we test for speed and accuracy. PyExoCross supports importing and exporting line lists in the ExoMol and HITRAN/HITEMP formats. PyExoCross also provides conversion between the ExoMol and HITRAN data format. In addition, PyExoCross has extra code for users to automate the batch download of line list files from the ExoMol database.

Effect of thermal annealing on the surface plasmon properties of gold and silver nanodisk structures fabricated by electron beam lithography

This study investigates the effect of thermal annealing on the surface plasmon resonance properties of gold and silver nanodisk structures fabricated by electron beam lithography. Despite no significant size change due to a nickel adhesion layer, thermal annealing at 500 °C notably altered surface plasmon resonance properties, especially in gold nanodisks, which showed peak blue-shifts and narrowing, indicating improved crystallinity. We fitted the peak shift by using an electromagnetic field analysis and discussed the changes in the dielectric function. The dielectric function of the simple Drude model was adopted, which was fitted to the values of the Lorentz Drude model in a limited wavelength region. While both silver and gold exhibited increased oscillation strength, only gold nanodisk structures showed a decrease in damping frequency. Increased oscillation strength indicated that these structures should be useful for selective enhancement of the light at specific wavelengths by a very simple heat treatment.

Dirac-Coulomb-Breit Molecular Mean-Field Exact-Two-Component Relativistic Equation-of-Motion Coupled-Cluster Theory.

We present a relativistic equation-of-motion coupled-cluster with single and double excitation formalism within the exact two-component framework (X2C-EOM-CCSD), where both scalar relativistic effects and spin-orbit coupling are variationally included at the reference level. Three different molecular mean-field treatments of relativistic corrections, including the one-electron, Dirac-Coulomb, and Dirac-Coulomb-Breit Hamiltonian, are considered in this work. Benchmark calculations include atomic excitations and fine-structure splittings arising from spin-orbit coupling. Comparison with experimental values and relativistic time-dependent density functional theory is also carried out. The computation of the oscillator strength using the relativistic X2C-EOM-CCSD approach allows for studies of spin-orbit-driven processes, such as the spontaneous phosphorescence lifetime.

Benford’s law in atomic spectra and opacity databases

The intriguing law of anomalous numbers, also named Benford’s law, states that the significant digits of data follow a logarithmic distribution favoring the smallest values. In this work, we test the compliance with this law of the atomic databases developed at the National Institute of Standards and Technology (NIST) focusing on line energies, oscillator strengths, Einstein coefficients and radiative opacities. The considered databases are the Atomic Spectra Database (ASD) and the NIST-LANL (Los Alamos National Laboratory) Lanthanide/Actinide Opacity Database. The present study is not limited to the first digit and the case of multipole lines is also considered. The fact that the law is verified with a high accuracy means that the occurrence of digits reflects the constraints induced, in a given angular-momentum coupling, by the selection rules for atomic processes. As a consequence, Benford’s law may be of great interest to detect inconsistencies in atomic databases.

Self-assembled crown ether (15CR5) with alkaline earth metals to stimulate nonlinear optical properties: The comprehensive study by silico technique

Crown Ether (15CR5) molecule is a worthwhile organic material exhibiting excellent NLO properties and characteristics. In this research, density functional theory (DFT) was extensively employed to study the nonlinear optical (NLO) properties of alkaline earth metal doped 15CR5 by using WB97XD/6-31G+(d, p). Binding energies, interaction energies, vertical ionization energies and reactivity parameters unveiled the thermodynamic stability of these systems. These molecules show a lower value of HUMO-LUMO energy gap indicating their superior electronic properties. Moreover, these complexes possess high oscillator strength and lower excitation energies displaying their better electrical and optical characteristics than pure 15CR5. Non-covalent analysis was carried out for all the designed systems forecasted the van der wall interactions between 15CR5 and dopants. These complexes in the visible region have excess electrons that are highly absorbed in the range of 405.73 to 608.27 compared to 15CR5. The Hyperpolarizability (βtot) of these designed materials was in the range of 9097.21–21627.85 au which is significantly higher than its pure counterpart. Results based on the density of state (DOS), natural bond orbital analysis (NBO) and transition density matrix (TDM) were also strongly supported the enhancement of the NLO properties of these systems. These newly designed alkaline earth metal doped 15CR5 systems with promising NLO characteristics can be used for optoelectronic applications.

Relativistic calculations of energy levels, lifetimes, transition parameters, and electron impact excitation cross sections for Kr XIX

In this study, we present a detailed analysis of atomic properties for Kr XIX, specifically focusing on the lowest 128 fine-structure levels originating from the 3s23p6, 3s23p53d, 3s3p63d and 3s23p43d2 configurations. We report energy levels, lifetimes, wavelengths, weighted oscillator strengths, and transition probabilities for multipole transition types (E1, E2, M1, and M2). To achieve this, we employed the GRASP2018 code, which implements the fully relativistic multiconfigurational Dirac–Hartree–Fock method and accounts for Breit interaction and quantum electrodynamic effects. We performed another set of calculations using the many-body perturbation theory implemented in the flexible atomic code (FAC). By comparing the results obtained from GRASP2018 and FAC, we established the accuracy and consistency of our calculations. Furthermore, using the relativistic distorted wave theory, we studied electron impact excitation of all transitions to upper levels from the ground and metastable levels and reported excitation cross sections for incident electron energies up to 5 keV. To enhance the practical utility of our findings, we also provided analytical fittings of these cross sections and excitation rate coefficients for their applications in plasma modeling. This work contributes to the atomic properties and excitation cross sections of Kr XIX, addressing a marked gap in the available atomic data.

Ab Initio Study on Electronic Excited States of Monochlorosilylene.

We perform a high-level ab initio study on 20 electronic states of monochlorosilylene (HSiCl) using an internally contracted multireference configuration interaction method including Davidson correction (icMRCI+Q). The spin-orbit coupling (SOC) effect is investigated, leading to splitting of the 20 spin-orbit-free states into 50 spin-orbit-coupled states. Vertical transition energies, oscillator strengths, and potential energy curves are presented with and without considering the SOC effect. Analysis indicates that the SOC effect plays an important role, especially for the high-lying excited states of HSiCl. The state interaction and the dynamics of the electronic states of HSiCl in the ultraviolet region are discussed based on our calculation results. Our study paves the way to understanding the behavior of electronic excited states of monochlorosilylene.

Influence of workpiece geometry and natural frequencies on ultrasonic metal welding

Ultrasonic metal welding is a well-established solid state joining process for electrical applications. The process relies on the friction between workpieces and welding tools for joint formation. This friction is generated by the process force and the ultrasonic oscillation of the welding tools imposed on the workpieces. At such high frequencies, the occurrence of resonances in actual workpiece geometries is not surprising. It is known that critical dimensions in length and width lead to nearly no bond, depending on the welding frequency and the mechanical properties of the material. In real applications, this limits the possible designs of terminals and leads to extensive testing of clamping devices. It is also known that machine learning (ML) models for quality prediction based on power signals or tool oscillation can account for changes in welding position. In this study, we investigated the impact of part resonance and antiresonance on horn and anvil oscillation, power consumption and bond strength to identify typical behaviors induced by the workpieces. The influence of material thickness and roughness was considered, and numerical analysis of the natural frequencies of the workpieces was conducted. It can be shown that the results allow a distinction between the welding positions and workpiece geometries without directly measuring the oscillation patterns of the workpieces, allowing a simple validation of geometry weldability and clamping device in applications. Furthermore, the investigation allows the knowledge based specific deduction of signal parameters for future ML models, allowing a consideration of welding position and workpieces geometry with reduced test data.

Judd-ofelt analysis and luminescent properties of the Dy3+-doped borosilicate glass

B2O3-SiO2-WO3-Ga2O3 glasses doped with Dy3+ were synthesized using the high-temperature melting method. The effects of different B2O3/SiO2 ratios, different Dy3+ ions doping concentrations, and alkali metal oxides on the glass structure and optical properties were investigated through the test methods of X-ray diffraction, differential scanning calorimetry, Fourier infrared spectra, and photoluminescence spectra. The oscillator strength and intensity parameters were determined using Judd-Ofelt theory, and the optical band gap for both indirect and direct allowed transitions were calculated. The glasses exhibited optimal luminous performance when the B2O3/SiO2 ratio was 50:33, Dy2O3 doping concentration was 0.5 mol%, and K2O concentration was 4 mol%, excited by a wavelength of 388 nm. The CIE coordinates falling within the white light region suggest the potential application of these glasses in white solid-state lighting.

Hybrid Moiré Excitons and Trions in Twisted MoTe2-MoSe2 Heterobilayers.

We report experimental and theoretical studies of MoTe2-MoSe2 heterobilayers with rigid moiré superlattices controlled by the twist angle. Using an effective continuum model that combines resonant interlayer electron tunneling with stacking-dependent moiré potentials, we identify the nature of moiré excitons and the dependence of their energies, oscillator strengths, and Landé g-factors on the twist angle. Within the same framework, we interpret distinct signatures of bound complexes among electrons and moiré excitons in nearly collinear heterostacks. Our work provides a fundamental understanding of hybrid moiré excitons and trions in MoTe2-MoSe2 heterobilayers and establishes the material system as a prime candidate for optical studies of correlated phenomena in moiré lattices.

Giant Faraday rotation in atomically thin semiconductors

Faraday rotation is a fundamental effect in the magneto-optical response of solids, liquids and gases. Materials with a large Verdet constant find applications in optical modulators, sensors and non-reciprocal devices, such as optical isolators. Here, we demonstrate that the plane of polarization of light exhibits a giant Faraday rotation of several degrees around the A exciton transition in hBN-encapsulated monolayers of WSe2 and MoSe2 under moderate magnetic fields. This results in the highest known Verdet constant of -1.9 × 107 deg T−1 cm−1 for any material in the visible regime. Additionally, interlayer excitons in hBN-encapsulated bilayer MoS2 exhibit a large Verdet constant (VIL ≈ +2 × 105 deg T−1 cm−2) of opposite sign compared to A excitons in monolayers. The giant Faraday rotation is due to the giant oscillator strength and high g-factor of the excitons in atomically thin semiconducting transition metal dichalcogenides. We deduce the complete in-plane complex dielectric tensor of hBN-encapsulated WSe2 and MoSe2 monolayers, which is vital for the prediction of Kerr, Faraday and magneto-circular dichroism spectra of 2D heterostructures. Our results pose a crucial advance in the potential usage of two-dimensional materials in ultrathin optical polarization devices.

Enhancement of the NORAD-Atomic-Data Database in Plasma

We report recent enhancements to the online atomic database at the Ohio State University, NORAD-Atomic-Data, that provide various parameters for radiative and collisional atomic processes dominant in astrophysical plasma. NORAD stands for Nahar Osu RADiative. The database belongs to the data sources, especially for the latest works, of the international collaborations of the Opacity Project and the Iron Project. The contents of the database are calculated values for energies, oscillator strengths, radiative decay rates, lifetimes, cross-sections for photoionization, electron-ion recombination cross-sections, and recombination rate coefficients. We have recently expanded NORAD-Atomic-Data with several enhancements over those reported earlier. They are as follows: (i) We continue to add energy levels, transition parameters, cross-sections, and recombination rates for atoms and ions with their publications. (ii) Recently added radiative atomic data contain a significant amount of transition data for photo-absorption spectral features corresponding to the X-ray resonance fluorescence effect, showing prominent wavelength regions of bio-signature elements, such as phosphorus ions, and emission bumps of heavy elements, such as of lanthanides, which may be created in a kilonova event. We are including (iii) collisional data for electron-impact-excitation, (iv) experimental data for energies and oscillator strengths for line formation, (v) experimental cross-sections for photoionization that can be applied for benchmarking and other applications, and (vi) the introduction of a web-based interactive feature to calculate spectral line ratios at various plasma temperature and density diagnostics, starting with our recently published data for P II. We presented a summary description of theoretical backgrounds for the computed data in the earlier paper. With the introduction of experimental results in the new version of NORAD, we present a summary description of measurement of high-resolution photoionization cross-sections at an Advanced Light Source of LBNL synchrotron set-up and briefly discuss other set-ups. These additions should make NORAD-Atomic-Data more versatile for various applications. For brevity, we provide information on the extensions and avoid repetition of data description of the original paper.