1s State Research Articles

Molybdenum Induced Modifications in the Quantum Capacitance of Graphene‐Based Supercapacitor Electrodes: First‐Principle Calculations

Herein, spin‐polarized calculation is performed based on density‐functional theory in the frame of generalized gradient approximation to examine the quantum capacitance (CQ) and surface charge storage of graphene(G)‐based supercapacitor electrodes modified with molybdenum, sulfur, nitrogen, and monovacancy. In total, 15 electrode models, including graphitic doping, monovacancy doping, and Mo adsorption on pristine and single‐vacancy graphene structures are analyzed. In the results, it is demonstrated that vacancy defects and N/S/Mo doping enhances the CQ of graphene. Among all configurations, pyrrolic‐S (d1S) shows the lowest CQ performance due to few states at the Fermi level. Electrodes with Mo adsorption exhibit the highest CQ, particularly when Mo is adsorbed at the top site of graphene. However, formation and adsorption energy calculations suggest that Mo is more likely to adsorb at hollow sites. Optimally, Mo can be most effectively utilized by loading it onto vacancy or N/S‐decorated vacancy sites. The significant contribution of Mo's 4dz2 and 4s states to CQ, along with the charge‐redistribution around the Mo complexes, may facilitate proton‐coupled electron transfer to enhance pseudocapacitance. In these findings, valuable insights into designing high quantum capacitance of 2D materials with electroactive sites for improved energy storage are offered.

Mixing effects on spectroscopy and partonic observables of heavy mesons with logarithmic confining potential in a light-front quark model

Using the variational principle, we systematically investigate the mass spectra and wave functions of both 1S and 2S state heavy pseudoscalar (P) and vector (V) mesons within the light-front quark model. This approach incorporates a Coulomb plus logarithmic confinement potential to accurately describe the constituent quark and antiquark dynamics. Additionally, spin hyperfine interactions are introduced perturbatively to compute the masses of pseudoscalar and vector mesons. The present analyses of the 1S and 2S states require the consideration of mixing between them to account for empirical constraints. These constraints include the mass gap ΔMP>ΔMV, where ΔMP(V)=MP(V)2S−MP(V)1S and the hierarchy of the decay constants f1S>f2S. We find the optimal value of the mixing angle to be θ=18°, significantly enhancing the consistency between our spectroscopic predictions and the experimental data compiled by the Particle Data Group. Furthermore, based on the predicted mass, the newly observed resonance BJ(5840) could be assigned as a 21S0 state in the B meson family. The study also reports various pertinent observables, including twist-two distribution amplitudes, electromagnetic form factors, charge radii, ξ moments, and transition form factors that are found to be consistent with both available lattice simulations and experimental data. In addition, our predicted branching ratios for the channels of B+→τ+ντ as well as rare decays of B0 and Bs0 appear in accordance with experimental data. Published by the American Physical Society 2024

Rotation effect on the spectral function of heavy vector mesons in holographic QCD

Abstract: Exploring heavy vector mesons of the J/ψ and ϒ(1S) is crucial for understanding the quark gluon plasma (QGP) formed in heavy ion collisions. The influences of rotational effect on the properties of the J/ψ and the ϒ(1S) are investigated by incorporating rotation medium into the holographic QCD. It is found that temperature, chemical potential, and rotational radius effects enhance the dissociation process of the J/ψ and the ϒ(1S) states within the medium. This rotation-induced effect is more significant for heavy vector mesons in the transverse direction than that of the longitudinal direction. The first holographic study on the influence of the radius of a homogeneous rotating system on the vector meson spectrum is proposed. It is found that increasing in rotation radius promotes the dissociation of vector mesons of the J/ψ and ϒ(1S). We also find that the dissociation perpendicular to the direction of rotational angular velocity is more significant than that parallel to it at large rational radius. Published by the American Physical Society 2024

Li decorated graphdiyne nanosheets: A theoretical study for an electrode material for nonaqueous lithium batteries

In this work, Density Functional Theory (DFT) is used to study pristine and defective GDY. We investigate the effect of Li atom adsorption on the electronic and structural properties of this 2D material. In both cases, the Li atom is located at the corner of the triangular‐like pore (H1), but with a slight shift for the defective system. In the perfect system, the Li‐C bond distances range from 2.289 Å to 2.461 Å, while in the defective case, they range from 2.237 Å to 3.184 Å. In the perfect case, the GDY‐Li system becomes metallic and the Li 2s states are stabilized. Charge transfer to the surfaces occurs near the vicinity of the Li atom. The C vacancy generates new C=C bonds similar to double bonds, enhancing the interaction with Li through strong conjugation. After Li adsorption, the sum of bond order for all the C atoms increases in both structures, from 0.4% to 6%. The Li storage capacity without significant restructuring is six Li atoms. When the atom concentration increases, the OCV values for Li decrease from 0.93 V to 0.23 V. For defective GDY, the specific capacity is 788 mAhg‐1, which is slightly higher than for pristine case.

Observation of reversible conformational interconversion accompanied by 3p internal conversions in Rydberg-excited N,N-dimethylethylamine

Conformational dynamics has been well observed in the 3s Rydberg state of amines, whereas its observation in higher-energy, non-equilibrium 3p Rydberg states is very rare, especially for a reversible conformational transition that could compete with other non-adiabatic transitions. Herein, we report the observation of a reversible conformational interconversion phenomenon in the 3p Rydberg excited-state dynamics of N,N-dimethylethylamine (DMEA). Upon electronic excitation, a forward and backward interconversion between the initially prepared 3p_l and 3p_h conformers accompanied by 3p internal conversions occurs, resulting in a 3p_l/3p_h equilibrium ratio of 61 %/39 % within ∼1.5 ps. The ensuing parallel internal conversions from the 3p_l to 3s_l and 3p_h to 3s_h deposit about 1.80 eV of vibrational energy into the 3s state, enabling a fast conformational interconversion between the 3s_h and 3s_l conformers to proceed within ∼2.0 ps. The final 3s_l/3s_h equilibrium ratio was determined to be 76 %/24 %. This work presents a real-time observation of the entire conformational interconversion process initiating from the higher-energy 3p states and finally reaching an equilibrium on the lower-energy 3s state.

Analysis of 2S singly heavy baryons in HQET

In this paper, we have employed HQET to determine the masses of radially excited ([Formula: see text]) S-wave charm and bottom baryons. The HQET Lagrangian containing the non-perturbative parameters is shown with heavy baryon fields. The non-perturbative parameters, couplings, and decay widths are also studied for the S-wave singly heavy baryons. The HQET parameters [Formula: see text], [Formula: see text] and [Formula: see text] are calculated for the ground state ([Formula: see text]) using the masses of S-wave baryons. The [Formula: see text] mass short-distance mass scheme is employed to estimate the heavy quark masses and non-perturbative parameters. The mass term ratios of [Formula: see text] and [Formula: see text] mesons and baryons containing parameters [Formula: see text] and [Formula: see text] are studied by varying the bottom quark mass. This analysis shows that heavy quarks behave the same inside mesons and baryons in both 1S and 2S states. The HQET symmetry of [Formula: see text] is used to find the parameters and masses for [Formula: see text] S-wave baryons. The variation of mass of 2S baryons with the non-perturbative parameters [Formula: see text] and [Formula: see text] is discussed. The Regge trajectories are also plotted in the [Formula: see text] plane using masses of [Formula: see text] and 2 charm and bottom baryons. The Regge trajectories are parallel and equidistant lines in the [Formula: see text] plane. We have also studied the strong decays of charm and bottom baryons for both [Formula: see text] and [Formula: see text] states. We have estimated the coupling constants [Formula: see text] and [Formula: see text] for [Formula: see text], and [Formula: see text] for [Formula: see text]. We have also shown the semi-electronic decay rates of charm baryons in the spectator heavy quark approximation for [Formula: see text], [Formula: see text], and [Formula: see text] transitions. The decay rates for [Formula: see text] transitions are of the same order as [Formula: see text] transitions. This analysis agrees well with the available theoretical and experimental data.

XPS Binding Energy Shifts in 2D Ti3C2Tz MXene go largely Beyond Intuitive Explanations: Rationalization from DFT Simulations and Experiments.

MXenes are prototypes of surface tunable 2D materials with vast potential for properties tuning. Accurately characterizing their surface functionalization and its role in electronic structure is crucial, X-ray photoelectron spectroscopy (XPS) being among the go-to methods to do so. Despite extensive use, XPS analysis remains however intricate. Focusing on the benchmark MXene Ti3C2Tz, Density Functional Theory (DFT) calculations of core-level binding energy shifts (BE.s.) are combined with experiments in order to provide a quantitative interpretation of XPS spectra. This approach demonstrates that BE.s. are driven by the complex interplay between chemical, structural, and subtle electronic structure effects preventing analysis from intuitive arguments or comparison with reference materials. In particular, it is shown that O terminations induce the largest BE.s. at Ti 2p levels despite lower electronegativity than F. Additionally, F 1s levels show weak sensitivity to the F local environment, explaining the single contribution in the spectrum, whereas O 1s states are significantly affected by the local surface chemistry. Finally, clear indicators of surface group vacancies are given at Ti 2p and O 1s levels. These results demonstrate the combination of calculations with experiments as a method of the highest value for MXenes XPS spectra analysis, providing guidelines for otherwise complex interpretations.

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.

Finite Nuclear Size Effect on the Relativistic Hyperfine Splittings of 2s and 2p Excited States of Hydrogen-like Atoms

Hyperfine splittings play an important role in quantum information and spintronics applications. They allow for the readout of the spin qubits, while at the same time providing the dominant mechanism for the detrimental spin decoherence. Their exact knowledge is thus of prior relevance. In this work, we analytically investigate the relativistic effects on the hyperfine splittings of hydrogen-like atoms, including finite-size effects of the nucleis’ structure. We start from exact solutions of Dirac’s equation using different nuclear models, where the nucleus is approximated by (i) a point charge (Coulomb potential), (ii) a homogeneously charged full sphere, and (iii) a homogeneously charged spherical shell. Equivalent modelling has been done for the distribution of the nuclear magnetic moment. For the 1s ground state and 2s excited state of the one-electron systems H1, H2, H3, and He+3, the calculated finite-size related hyperfine shifts are quite similar for the different structure models and in excellent agreement with those estimated by comparing QED and experiment. This holds also in a simplified approach where relativistic wave functions from a Coulomb potential combined with spherical-shell distributed nuclear magnetic moments promises an improved treatment without the need for an explicit solution of Dirac’s equation within the nuclear core. Larger differences between different nuclear structure models are found in the case of the anisotropic 2p3/2 orbitals of hydrogen, rendering these excited states as promising reference systems for exploring the proton structure.

Theoretical study of differential cross sections for the ionization of helium by fast proton impact

Abstract We present the angular distribution of the ejected electron for single ionization of He by fast proton impact. A four-body formalism of the three-Coulomb wave is applied to calculate the triple differential cross sections at several impact energies in the scattering, perpendicular and azimuthal planes. Moreover, the three-body formalism of three-Coulomb, two-Coulomb and first Born approximation models has also been used to study the many-body effect on electron emission and the validity of the models. In the three-Coulomb wave model, the final state wave function incorporates distortion due to the three-body mutual Coulombic interaction. In this formalism, we use an uncorrelated and correlated Born initial state, which consists of a plane wave for the incoming projectile times a two-electron bound state wavefunction of the helium atom representing the 1s2(1S) state. But, in the case of the three-body formalism, the initial state wavefunction consists of a long-range Coulomb distortion for the incoming projectile and one active electron of the He atom described by the Roothaan–Hartree–Fock wavefunction. The structure with a single or two peaks with unequal intensity is observed in the angular distributions of the triple differential cross sections for the different kinematic conditions. In addition, the influence of static electron correlations is investigated using different bound state wavefunctions for the ground state of the He target. In the four-body formalism, the present computations are very fast by reducing a nine-dimensional integral to a two-dimensional real integral. Despite the simplicity and speed of the proposed quadrature, the comparison shows that the obtained results are in reasonable agreement with the experiment and are compatible with those of other theories.

Improvement of BGO ceramic scintillators through hot‐pressing sintering methodology

AbstractIn the present work, the sintering of bismuth germanate through hot pressing and the improvement of scintillator performance were investigated. The linear shrinkage, crystalline structure, microstructure, transparency degree, and radioluminescence (RL) were studied as functions of the sintering pressure. X‐ray diffraction revealed that the samples were predominantly composed of the Bi4Ge3O12 phase, accompanied by small amounts of Bi12GeO20, with concentrations varying according to the sintering parameters. These concentrations were quantified through Rietveld refinement, which also indicated a tendency for the cell parameters to shrink as the sintering pressure increased. The microstructure of the ceramic pellets produced under varying hot‐pressing parameters was investigated using scanning electron microscopy (SEM), revealing that while the grain size was preserved, the porosity and grain boundary thickness were reduced by the hot pressing, forming a quasicontinuum in some areas of the sample. The RL of all the samples exhibited a green color, with a maximum at 540 nm, ascribed to the transitions from the 3P0,1,21P1 excited states to the fundamental 1S0 state of the Bi3+ ions. For samples sintered under a pressure of .18 MPa, the enhancement in the optical transmittance, accompanied by a 61.36% increase in light output at the maximum wavelength, was observed.

The Effect of Silicon Substitution by Boron for the α-Nb5Si3: INSIGHTS into the Constitutive Properties of Nb5Si2B Through Theory and Experimental Approach

We investigated the structural, elastic, vibrational, and electronic properties of the Nb5Si2B compound combining density functional theory (DFT) calculations and experimental methods. We compared our results with the parent compound Nb5Si3 with two non-equivalent Si sites namely Si(4a) and Si(8h). The analysis of elastic constants and phonon spectra indicate that Nb5Si2B is respectively mechanically and dynamically stable. Based on the phonon calculation we evaluate the theoretical constant volume lattice specific heat (CV) for different site occupancies and compare it with experimental specific heat (Cp) measurements. We found an excellent agreement between theoretical and experimental results for Nb5Si2B with the B at the Si(8h) site, which agrees with the calculated formation energy. In addition, we also performed DFT calculations aimed at showing and comparing the total DOS near the Fermi level (EF) for Nb5Si3 and Nb5Si2B. The XPS valence band (VB) of the Nb5Si2B is largely dominated by two characteristic peaks at − 8.7 and − 1.7 eV, respectively. Based on DFT calculations, it follows that the main sharp peak at − 1.7 eV comes as a contribution from Nb 4d states, while the smaller and broader one located at − 8.7 eV results mainly from Si 3s states weakly hybridized with Nb 4d states. In this connection, the majority contribution in the binding energy range from − 12 eV to the EF comes from Nb 4d states, while the contribution from Si and B atoms is very small in this region. The core levels of Nb 3d, Si 2s, 2p, and B 1s were also identified using the XPS technique.

Nuclear Structure Effects on Hyperfine Splittings in Ordinary and Muonic Deuterium.

Precision spectroscopy of hyperfine splitting (HFS) is a crucial tool for investigating the structure of nuclei and testing quantum electrodynamics. However, accurate theoretical predictions are hindered by two-photon exchange (TPE) effects. We propose a novel formalism that accounts for nuclear excitations and recoil in TPE, providing a model-independent description of TPE effects on HFS in light ordinary and muonic atoms. Combining our formalism with pionless effective field theory at next-to-next-to-leading order, the predicted TPE effects on HFS are 41.7(4.4)kHz and 0.117(13)meV for the 1S state in deuterium and the 2S state in muonic deuterium. These results align within 1σ and 1.3σ from recent measurements and highlight the importance of nuclear structure effects on HFS and indicate the value of more precise measurements in future experiments.

Geometrical, elastic, electronic, phonon, and optical properties of Na3AgO2 from first-principles calculation

In this paper, the geometrical, elastic, electronic, phonon, and optical properties of Na3AgO2 have been systematically studied by first-principles calculation. The results show that Na3AgO2 is mechanically stable and has small compressibility. Na3AgO2 is an indirect band-gap semiconductor with weak interatomic interaction. The bandgap calculated by HSE06 is 2.314 eV, and that calculated by GGA is 1.261 eV. For Na3AgO2, in the valence band near the Fermi level, the curve peaks of TDOS at −2.11 eV and −0.885 eV are primarily composed of O 2p states, which hybridize the 4 d and 4p states of Ag. The conduction band mainly consists of the 4p, 4 d, and 5s states of Ag, while hybridizing a few 2p states of O and a few 2p and 3s states of Na. As can be seen from the phonon dispersion spectrum there is no negative phonon frequency in the whole Brillouin region, indicating the structure is stable. Mulliken bond population of Na3AgO2 shows that O–Ag bonds have strong covalency, O–Na bonds have strong ionic properties, Na–Na bonds and Na–Ag bonds are antibonding. Na3AgO2 has a small reflectivity and a small absorption coefficient in the direction of (100) and (010) and has good transparency. The transparency of blue-violet light in the (001) direction is not as good as that of low-energy visible light. The obtained results lead to the conclusion that Na3AgO2 is a promising p-type transparent conducting material and is expected to be applied in practice.

Investigating quantum coherence of N-methylpyrrole through vibrational spectroscopy and potential energy: A theoretical study

Quantum chemical calculations are utilized to analyze the potential causes of N-methylpyrrole oscillations, focusing on vibration spectra and potential energy curves. Optimization of the ground state, ionic state and 3s state structure reveal mostly sp2 hybridization. An analysis of the 3s state vibration spectrum and adiabatic binding energy indicate that changes in dihedral angles D2,3,4,1 and plane angle A3,2,1 are potential factors contributing to molecular oscillations. The role of vertical binding energy and adiabatic binding energy in the oscillation process are also discussed, shedding light on the possible dynamic processes of N-methylpyrrole.

Spin-orbit coupling in excited electronic states of AgH

Potential energy curves have been calculated for the low-lying electronic states of AgH, correlating to the 4d10 5s1 (2S), 4d10 5p1 (2Po), 4d9 5s2 (2D), and 4d10 6s1 (2S) states of atomic silver, using the MRCI method with scalar relativistic and spin–orbit corrections. Spectroscopic constants were obtained for 24 individual Ω states, and several excited states of AgH observed in the ultraviolet absorption spectra, i.e., the C1Π, B1Σ+, b3Δ1, and D1Π states, were relabeled based on the new ab initio data. The calculated Einstein A coefficients indicated that almost all electronic transitions with ΔΩ = 0, ±1 are allowed.

Ultrafast conformation-dependent charge transfer in N, N, N′, N′-tetramethyl-1,3-propanediamine: Effect of flexible carbon skeleton on electron lone pair interactions

Flexible three-carbon skeleton makes N, N, N′, N′-tetramethyl-1,3-propanediamine (TMPDA) an important diamine system to investigate the conformation-dependent electron lone pair interactions and charge delocalization. The charge transfer process linked to structural motions of the three-carbon skeleton has been monitored in real time by the Rydberg electron binding energy (BE) spectra of TMPDA coupled with quantum chemical calculations. Optical excitation to the 3p state with a 200 nm pump pulse initially generated a localized charge on one of the two nitrogen atoms that may partially transfer to the other one. Rapid internal conversion (IC) from the 3p to 3s state occurred within 430 fs, resulting in an initial charge delocalized 3s_h/3s_l population ratio of 23.6 %/76.4 %. A final 3s_h/3s_l (51.9 %/48.1 %) equilibrium proceeded within about 2.64 ps. The 3s_h (TTTT+, GG′TG+ and G′GG′G+) and 3s_l (GG′GG′+ and GG′G′G+) (see text for structure definitions) are identified as the extended and folded conformers, respectively. Two types of electron lone pair interactions, i.e., through-space interaction (TSI) and through-bond interaction (TBI), are found to coexist in TMPDA to drive charge transfer. The GG′GG′+ and GG′G′G+ structures exhibit TSI, while the TTTT+ structure shows TBI. The GG′TG+ and G′GG′G+ structures exhibit both TSI and TBI. Flexible three-carbon skeleton provide more opportunities for the two N-electron lone pairs to overlap in space (i.e., TSI), making TMPDA to be favorable for the most stably folded conformation.

Interlayer Fermi Polarons of Excited Exciton States in Quantizing Magnetic Fields.

The study of exciton polarons has offered profound insights into the many-body interactions between bosonic excitations and their immersed Fermi sea within layered heterostructures. However, little is known about the properties of exciton polarons with interlayer interactions. Here, through magneto-optical reflectance contrast measurements, we experimentally investigate interlayer Fermi polarons for 2s excitons in WSe2/graphene heterostructures, where the excited exciton states (2s) in the WSe2 layer are dressed by free charge carriers of the adjacent graphene layer in the Landau quantization regime. First, such a system enables an optical detection of integer and fractional quantum Hall states (e.g., ν = ±1/3, ±2/3) of monolayer graphene. Furthermore, we observe that the 2s state evolves into two distinct branches, denoted as attractive and repulsive polarons, when graphene is doped out of the incompressible quantum Hall gaps. Our work paves the way for the understanding of the excited composite quasiparticles and Bose-Fermi mixtures.

Probing Collins Conjecture with correlation energies and entanglement entropies for the ground and excited states in the helium iso‐electronic sequence

AbstractIn the present work, we present an investigation of Collins Conjecture, a hypothesis made by D. M. Collins in 1993 relating correlation energy and entanglement entropy, by calculating the ground state and singly‐excited triplet‐spin 1s2s 3S and 1s3s 3S state energies of the helium iso‐electronic sequence, with Z = 2–15. By using extensive orthonormal configuration interaction (CI) type wave functions with B‐Spline basis up to about 6000 terms, linear entropy and von Neumann entropy for the abovementioned atomic systems are determined. Together with the Hartree‐Fock energies obtained following a self‐consistent field theory, we have found that there exist linearly proportionalities between the renormalized correlation energies and entanglement entropies of both linear and von Neumann, showing a support for Collins Conjecture applicable to the ground and singly‐excited triplet‐spin states in the helium sequence, for a range of finite Z‐values.

Amorphous MoS2 from a machine learning inter-atomic potential.

Amorphous molybdenum disulfide has shown potential as a hydrogen evolution catalyst, but the origin of its high activity is unclear, as is its atomic structure. Here, we have developed a classical inter-atomic potential using the charge equilibration neural network method, and we have employed it to generate atomic models of amorphous MoS2 by melting and quenching processes. The amorphous phase contains an abundance of molybdenum and sulfur atoms in low coordination. Besides the 6-coordinated molybdenum typical of the crystalline phases, a substantial fraction displays coordinations 4 and 5. The amorphous phase is also characterized by the appearance of direct S-S bonds. Density functional theory shows that the amorphous phase is metallic, with a considerable contribution of the 4-coordinated molybdenum to the density of states at the Fermi level. S-S bonds are related to the reduction of sulfur, with the excess electrons spread over several molybdenum atoms. Moreover, S-S bond formation is associated with a distinctive broadening of the 3s states, which could be exploited for experimental characterization of the amorphous phases. The large variety of local environments and the high density of electronic states at the Fermi level may play a positive role in increasing the electrocatalytic activity of this compound.