Ground State Values Research Articles

A proton-coupled electron transfer process from functionalized carbon dots to molecular substrates: the role of pH.

Multiple electron and proton transfers in nanomaterials pose significant demands and challenges across the various fields such as renewable energy, chemical processes, biological applications, and photophysics. In this context, pH-responsive functional group-enriched carbon dots (C-Dots) emerge as superior proton-coupled electron transfer (PCET) agents owing to the presence of multiple functional groups (-COOH, -NH2, and -OH) on the surface and redox-active sites in the core. Here, we elucidate the 2e-/2H+ transfer ability of carboxyl-enriched C-Dots (C-Dot-COOH) and amine-enriched C-Dots (C-Dot-NH2) with molecular 2e-/2H+ acceptor (benzoquinone, BQ) as a function of pKa, facilitated by the formation of new O-H bonds. The ground state and excited state pKa values of different functional groups on the surface of C-Dots are determined using steady-state absorbance and photoluminescence (PL) spectroscopy. The optical spectroscopy and electrochemical studies are employed to comprehend the influence of the surface and core of C-Dots on the proton and electron transfer processes as a function of pH. The cyclic voltammetry analysis reveals a standard Nernstian shift in E1/2 per pH unit of 30 mV, indicating that the functionalized C-Dots hold promise as candidates for the 2e-/2H+ transfer process. The calculated bond dissociation free energy (BDFE) of the electroactive O-H/N-H bonds provides a more nuanced and detailed understanding of PCET thermodynamic landscapes. These findings underscore the potential of nanoscale functionalized C-Dots for facilitating multiple PCET reactions in future energy technologies.

Numerical linked-cluster expansions for two-dimensional spin models with continuous disorder distributions.

We show that numerical linked cluster expansions (NLCEs) based on sufficiently large building blocks allow one to obtain accurate low-temperature results for the thermodynamic properties of spin lattice models with continuous disorder distributions. Specifically, we show that such results can be obtained computing the disorder averages in the NLCE clusters before calculating their weights. We provide a proof of concept using three different NLCEs based on L, square, and rectangle building blocks. We consider both classical (Ising) and quantum (Heisenberg) spin-1/2 models and show that convergence can be achieved down to temperatures that are up to two orders of magnitude lower than the relevant energy scale in the model. Additionally, we provide evidence that in one dimension one can obtain accurate results for observables such as the energy down to their ground-state values.

A new family of heterometallic [Cu6M4] (M = Gd, Tb, Dy and Y) clusters derived from the combined use of selected pyridyl poly-alcohol ligands.

The combined use of 2-(2-pyridyl)-1,3-propane-diol (pypdH2) and 2-hydroxymethyl-2-(2-pyridyl)-1,3-propane-diol (pyptH3) in Cu2+/4f chemistry has afforded a new family of isostructural [Cu6M4(pypt)4(pypdH)4(NO3)8] [M = Gd (1), Tb (2), Dy (3), and Y (4)] complexes. These compounds are based on an unprecedented three-layered symmetric [Cu6M4(μ-OR)16]8+ structural core, formed from the connection of the metal ions by bridging alkoxide arms of the organic ligands. Direct current magnetic susceptibility studies for complexes 1-3 revealed the presence of dominant ferromagnetic exchange interactions, suggesting the existence of large spin ground state values. Alternating current magnetic studies indicate the presence of slow-magnetic relaxation in 1-3.

Performance of the COSMO solvation model for photoacidity and basicity in water.

The possibilities and problems to predict excited-state acidities and basicities in water with electronic structure calculations combined with a continuum solvation model are investigated for a test set of photoacids and photobases. Different error sources, like errors in the ground-state values, the excitation energies in solution for the neutral and (de-)protonated species, basis set effects, and contributions beyond implicit solvation are investigated and their contributions to the total error in are discussed. Density functional theory in combination with the conductor like screening model for real solvents and an empirical linear Gibbs free energy relationship are used to predict the ground-state values. For the test set, this approach gives more accurate values for the acids than for the bases. Time-dependent density-functional theory (TD-DFT) and second-order wave function methods in combination with the conductor like screening model are applied to compute excitation energies in water. Some TD-DFT functionals fail for several species to predict correctly the order of the lowest excitations. Where experimental data for absorption maxima in water is available, the implicit solvation model leads with the applied electronic structure methods in most cases for the excitation energies in water to an overestimation for the protonated and to an underestimation for the deprotonated species. The magnitude and sign of the errors depend on the hydrogen bond donating and accepting ability of the solute. We find that for aqueous solution this results generally in an underestimation in the changes from the ground to the excited state for photoacids and an overestimation for photobases.

Molecular engineering on D-π-A organic dyes with flavone-based different acceptors for highly efficient dye-sensitized solar cells using experimental and computational study

The improvement of new organic flavone-based donor-spacer-acceptor (D-π-A) type dye molecules of the 3-(4-hydroxypiperidin-2-yloxy)-7-hydroxy-2-(3,4-dihydroxyphenyl)-4H-chromen-4-one (D1), 7-hydroxy-2-(3,4-dihydroxyphenyl)-3-(piperidin-4-yloxy)-4H-chromen-4-one (D2), and 3-((2-aminopyridin-4-yloxy)methoxy)-7-hydroxy-2-(3,4-dihydroxyphenyl)-4H-chromen-4-one (D3) were successfully designed and synthesized for dye-sensitized solar cells (DSSCs). Here, we discuss the synthesis of flavone compounds as well as their photophysical and electrochemical characterization. Using the Gaussian 09w software, the electronic structures and apsorption spectra have been calculated at the B3LYP, B3PW91, CAM-B3LYP, MPW1PW91, PBEPBE, and ωB97XD theory with the 6-311G(d,p) basis sets. The computed values of the D2 molecule ground state optimized HOMOs-LUMOs energy is well positioned for advantageous charge transfer (CT) into the semiconducting material (TiO2) as well as the electron injection process. With a high power conversion efficiency (PCE) of 3.46% (VOC = 0.718V, JSC = 7.07mAcm-2, and FF = 0.68), the D2 compound also demonstrated good photovoltaic (PV) properties. These findings unequivocally demonstrate that altering the D-π-A metal-free organic material electron-withdrawing capacity is a useful strategy for enhancing the optical and electrical characteristics of the organic PV system.

Resonant double-core excitations with ultrafast, intense X-ray pulses

Intense few-to-sub-femtosecond soft X-ray pulses can produce neutral, two-site excited double-core-hole states by promoting two core electrons to the same unoccupied molecular orbital. We theoretically investigate double nitrogen K-edge excitations of nitrous oxide (N 2 O) with multiconfigurational electronic structure calculations. We show that the second core-excitation energy is reduced with respect to its ground state value. A site-selective double core-excitation mechanism using intense few-femtosecond x-rays is investigated using time-dependent Schrödinger equation (TDSE) simulations. The subsequent two-step Auger–Meitner and two-electrons-one-electron decay spectra of the double core-excited states are analysed using a Mulliken population analysis of the multiconfirational wavefunctions. The change in the electron emission lineshape between the absorption of 1 or 2 photons in the resonant core-excitation is predicted by combining this approach with the TDSE simulations. We examine the possibility of resolving the double core-excited states with X-ray pump-probe techniques by calculating the chemical shifts of the core-electron binding energy of the core-excited states and decay products.

The effective theory of gravity and dynamical vacuum energy

Gravity and general relativity are considered as an Effective Field Theory (EFT) at low energies and macroscopic distances. The effective action of the conformal anomaly of light or massless quantum fields has significant effects on macroscopic scales, due to associated light cone singularities that are not captured by an expansion in local curvature invariants. A compact local form for the Wess-Zumino effective action of the conformal anomaly and stress tensor is given, requiring the introduction of a new light scalar field, which it is argued should be included in the low energy effective action for gravity. This scalar conformalon couples to the conformal part of the spacetime metric and allows the effective value of the vacuum energy, described as a condensate of an exact 4-form abelian gauge field strength F = dA, to change in space and time. This is achieved by the identification of the torsion dependent part of the Chern-Simons 3-form of the Euler class with the gauge potential A, which enters the effective action of the conformal anomaly as a J · A interaction analogous to electromagnetism. The conserved 3-current J describes the worldtube of 2-surfaces that separate regions of differing vacuum energy. The resulting EFT thus replaces the fixed constant Λ of classical gravity, and its apparently unnaturally large sensitivity to UV physics, with a dynamical condensate whose ground state value in empty flat space is Λeff = 0 identically. By allowing Λeff to vary rapidly near the 2-surface of a black hole horizon, the proposed EFT of dynamical vacuum energy provides an effective Lagrangian framework for gravitational condensate stars, as the final state of complete gravitational collapse consistent with quantum theory. The possible consequences of dynamical vacuum dark energy for cosmology, the cosmic coincidence problem, and the role of conformal invariance for other fine tuning issues in the Standard Model are discussed.

Effect of double-constrained potential on the ground-state binding energy of magnetopolaron in a quantum well

This study aims at investigating the properties of magnetopolarons (MPs) in III–V compound semiconductors: GaP, GaAs and GaSb crystals. The obtained results from numerical calculation revealed that absolute value of ground-state (GS) binding energy [Formula: see text] of the magnetopolaron is affected by magnetic field, type of crystal as well as the parabolic and asymmetric Gaussian potentials, which leads to a series of interesting phenomena. The study of results obtained provides a good theoretical guidance on optoelectronic devices and quantum information. We have theoretically investigated the origins of these strange phenomena, and our findings provide sound theoretical direction for photoelectric technology and quantum information.

Fock-space perturbed relativistic coupled-cluster theory for electric dipole polarizability of one-valence atomic systems: Application to Al and In

We have developed a Fock-space relativistic coupled-cluster theory based method for the calculation of electric dipole polarizability of one-valence atoms and ions. We employ this method to compute the ground-state and spin-orbit coupled excited state electric dipole polarizability of Al and In. To check the quality of many-electron wavefunctions, we also compute the excitation energies of some low-lying states of Al and In. The effects of Breit interaction and QED corrections from the Uehling potential and the self-energy are included to improve the accuracy of $\alpha$ further. Our recommended value of ground-state $\alpha$ for both atoms are in good agreement with the previous theoretical results. From our computations, we find that more than 65\% of contributions come from the dipolar mixing of $3p$($5p$) with $3d$($5d$) and $4s$($6s$)-electrons for Al(In). The largest Breit and QED contributions are found to be 1.3\% and 0.6\%, respectively.

Precision Many-Body Study of the Berezinskii-Kosterlitz-Thouless Transition and Temperature-Dependent Properties in the Two-Dimensional Fermi Gas.

We perform large-scale, numerically exact calculations on the two-dimensional interacting Fermi gas with a contact attraction. Reaching much larger lattice sizes and lower temperatures than previously possible, we determine systematically the finite-temperature phase diagram of the Berezinskii-Kosterlitz-Thouless (BKT) transitions for interaction strengths ranging from BCS to crossover to BEC regimes. The evolutions of the pairing wave functions and the fermion and Cooper pair momentum distributions with temperature are accurately characterized. In the crossover regime, we find that the contact has a nonmonotonic temperature dependence, first increasing as temperature is lowered, and then showing a slight decline below the BKT transition temperature to approach the ground-state value from above.

Excited-state exchange interaction in NiO determined by high-resolution resonant inelastic x-ray scattering at the Ni M2,3 edges

The electronic and magnetic excitations of bulk NiO have been determined using the ${}^{3}{A}_{2g}$ to ${}^{3}{T}_{2g}$ crystal-field transition at the Ni ${M}_{2,3}$ edges with resonant inelastic x-ray scattering at 66.3- and 67.9-eV photon energies and 33-meV spectral resolution. Unambiguous assignment of the high-energy side of this state to a spin-flip satellite is achieved. We extract an effective exchange field of $89\ifmmode\pm\else\textpm\fi{}4$ meV in the ${}^{3}{T}_{2g}$ excited final state from empirical two-peak spin-flip model. The experimental data is found consistent with crystal-field model calculations using exchange fields of 60--100 meV. Full agreement with crystal-field multiplet calculations is achieved for the incident photon energy dependence of line shapes. The lower exchange parameter in the excited state as compared to the ground-state value of 120 meV is discussed in terms of the modification of the orbital occupancy (electronic effects) and of the structural dynamics: (A) With pure electronic effects, the lower exchange energy is attributed to the reduction in effective hopping integral. (B) With no electronic effects, we use the $S=1$ Heisenberg model of antiferromagnetism to derive a second-nearest-neighbor exchange constant ${J}_{2}$ = $14.8\ifmmode\pm\else\textpm\fi{}0.6$ meV. Based on the linear correlation between ${J}_{2}$ and the lattice parameter from pressure-dependent experiments, an upper limit of 2% local Ni-O bond elongation during the femtosecond scattering duration is derived.

Beetroot's crude aqueous extract photosensitizer-Formic acid-Sodium Lauryl Sulphate photogalvanic electrolyte: Solar power and storage

Crude aqueous extract of Beetroot has been used as a natural photo-sensitizer for photogalvanic solar power and storage. Beet's root extract-based photogalvanic cell shows improved electrical performance (power 674.4 μW, efficiency 15.31%) and follow the same principles as followed by synthetic photo-sensitizers based photogalvanics. Betalains have been characterized as the main light-absorbing molecules present in the extract. The concentrations and photo-thermal stability of Betalains have been studied for their future perspective. The estimated ground state and excited state potential values (vs NHE) of Betalain are as 0.9015 V and 1.3565 V, respectively, and it matches the published data. On the basis of standard reduction potential and electrochemical series, it is established that the reductant donates an electron to the excited state of pigment, and ground-state Betalain pigment donates an electron to the reductant. The same pattern of electron transfer is also reported for earlier photogalvanics.

Schrödinger-Poisson solitons: Perturbation theory

Self-gravitating quantum matter may exist in a wide range of cosmological and astrophysical settings from the very early universe through to present-day boson stars. Such quantum matter arises in a number of different theories, including the Peccei-Quinn axion and UltraLight (ULDM) or Fuzzy (FDM) dark matter scenarios. We consider the dynamical evolution of perturbations to the spherically symmetric soliton, the ground state solution to the Schr\"{o}dinger-Poisson system common to all these scenarios. We construct the eigenstates of the Schr\"{o}dinger equation, holding the gravitational potential fixed to its ground state value. We see that the eigenstates qualitatively capture the properties seen in full ULDM simulations, including the soliton "breathing" mode, the random walk of the soliton center, and quadrupolar distortions of the soliton. We then show that the time-evolution of the gravitational potential and its impact on the perturbations can be well described within the framework of time-dependent perturbation theory. Applying our formalism to a synthetic ULDM halo reveals considerable mixing of eigenstates, even though the overall density profile is relatively stable. Our results provide a new analytic approach to understanding the evolution of these systems as well as possibilities for faster approximate simulations.

Bimodal-random field Blume–Capel model in the cluster variation method

The outcome of the bimodal random magnetic field acting up or down along the z-axis on the spins of spin-1 with equal probability is investigated by using the lowest approximation of the cluster-variation method in the Blume–Capel model. The equal probability, p=12, causes the model to give phase transitions of the form either second- or first-order. The phase diagrams of the model are computed on the (D,kBT/J) and (h,kBT/J) planes by taking into account the thermal variations of the order-parameters. The obtained phase diagrams reveal different phase regions with ground state values of 1 and 1/2 in addition to tricritical and critical end points. Simple and double hysteresis loops are also observed in the model.

Electronic, magnetic and elastic calculations on half-metallic Heusler Ti2RuTl compound

ABSTRACT Electronic, magnetic and elastic calculations of a new Ti2RuTl full Heusler compound have been made using the Vienna Ab-initio Simulation Package (VASP). The computations were carried out for the ferromagnetic (FM) state in the F-43 m (No.216) space group. Ground-state values of the lattice parameter, bulk modulus, volume and energy were obtained. The lattice parameter of the cubic structure was 6.478 Å. According to the electronic calculations, the spin-up electrons were found to have metallic properties while the spin-down electrons were found to have a semiconductor nature. Therefore, these metallic and semiconductor spin states showed that the Ti2RuTl full Heusler compound is a half-metallic (HM) ferromagnet with 1.00 µB/f.u. magnetic moment. Finally, the elastic calculations showed that the compound is an elastically stable, ductile material and could be a new candidate material for using in spintronics.

A heterometallic [Mn9Ni2] cluster consisting of the [M4(μ3-O)3(μ3-Cl)]n+ cubane and [MnIII3(μ3-O)4]+ “V-shaped” sub-units appearing in the giant [Mn84] and [Mn70] compounds and its [Mn9CoIII2] analogue

Two new heterometallic clusters exhibiting related cores, [Mn9Ni2(μ3-Ο)10(μ3-Cl)2(O2CMe)11(py)4(H2O)4]·2H2O (1·2H2O) (py = pyridine) and [Mn9Co2(μ3-Ο)10(μ3-ΟΗ)2(O2CEt)10(EtOH)3(H2O)(py)5](ClO4)2Cl (2) are reported. Compounds 1·2H2O/2 were prepared from reactions of [Mn3O(O2CMe)6(py)3]·py/[Mn3O(O2CEt)6(py)3](ClO4) with MCl2·6H2O (M = Ni2+, Co2+) and (Bun4N)MnO4 in a 1:3:0.1/1:1:0.1 molar ratio in MeCN (15 ml)/MeOH-EtOH (15–0.5 ml) in ∼ 28 %/< 2 % yields, respectively. Their cores consist of two [MnIVMnIII2Mn+(μ3-Ο)3(μ3-X)]m+ cubanes (Mn+ = Ni2+, X = Cl−, m = 5+, 1·2H2O; Mn+ = Co3+, X = OH−, m = 6+, 2) at the terminal positions linked through a central [MnIII3(μ3-Ο)4]+ slightly V-shaped sub-unit. Interestingly, this core has appeared as a fragment in the giant [Mn84] and [Mn70] torus–like single–molecule magnets (SMMs). Magnetism studies of 1·2H2O revealed the presence of competing ferromagnetic and antiferromagnetic exchange interactions leading to a fairly low spin ground state value of ST ≈ 4 or 3 and fully visible out-of-phase ac signals (above 1.8 K) indicative of slow relaxation of the magnetization and SMM behavior.

Moduli and graviton production during moduli stabilization

In theories beyond the Standard Model, in particular in theories with extra spatial dimensions such as superstring theory, there are a large number of scalar fields which appear in the low energy effective action. These moduli fields must be stabilized. Often, moduli stabilization involves a stage during which the moduli fields oscillate coherently about their ground state value. Here, we study moduli and graviton production during the period during which the background modulus field is oscillating, assuming that this period takes place in the radiation phase. We find a resonant production of moduli fluctuations, and a tachyonic instability to the generation of long wavelength gravitational waves. As a consequence, the period of moduli stabilization is short on a Hubble time scale.

Synthesis, solvatochromism and electric dipole moment study of coumarin-fused quinoline: experimental and quantum chemical computational investigations

A new coumarin-fused quinoline push–pull fluorescent probe was designed, synthesized and characterized using $$^{\mathrm {1}}$$ H NMR, $$^{\mathrm {13}}$$ C NMR and mass spectrometry analysis. Electronic absorption and fluorescence studies of the synthesized probe were investigated in wide range of solvents of varying polarities, and the data were used to study its solvatochromic properties. The ground and excited state dipole moments of fluorescent probe were obtained from Bakhshiev’s and Bilot–Kawasaki’s equations by means of the solvatochromic shift method. The high value of dipole moment for the excited state over ground-state value was attributed to more polar excited state of molecule. Also, emission peak undergoes a bathochromic shift with an increase in the polarity of the solvent, confirming $${\varvec{\pi }} \rightarrow {\varvec{\pi }}{} \mathbf * $$ transition. The ground-state and excited-state dipole moments were calculated and compared using DFT calculations. Both experimental and computational studies revealed that excited-state dipole moment values are higher than corresponding ground-state value of studied compound. A new coumarin-fused quinoline push–pull fluorescent probe was designed, synthesized and characterized. The ground-state and excited-state dipole moments were calculated and compared using DFT calculations.

Ground-State Properties of Even–Even Nuclei from He (Z = 2) to Ds (Z = 110) in the Framework of Skyrme–Hartree–Fock–Bogoliubov Theory

The ground-state properties of 2094 even–even nuclei with $$2\le Z\le 110$$ over a wide range of isotopes have been calculated and studied in the framework of the Hartree–Fock–Bogoliubov (HFB) theory with the SKI3 Skyrme type effective nucleon–nucleon interaction. The calculated ground-state values of the binding energy per nucleon (B.E/A), quadrupole deformation parameter (β2), two-neutron separation energy (S2n), charge radii (RC), proton rms radii, neutron rms radii and neutron pairing gap have been compared with the available experimental data of the atomic mass evaluation (AME2016), the results of Hartree–Fock–Bogoliubov calculations based on the D1S Gogny effective nucleon–nucleon interaction and predictions of some nuclear models such as the finite range droplet model (FRDM2012) and relativistic mean-field model. Based on the HFBTHO results, the parameters of the Skyrme SKI3-HFB method can be successfully used for describing the ground-state properties of the investigated nuclei, in particularly the neutron-rich nuclei and the exotic nuclei near the neutron drip-line.

Magnetic phase transitions in two-dimensional two-valley semiconductors with in-plane magnetic field

A two-dimensional electron gas (2DEG) in two-valley semiconductors has two discrete degrees of freedom given by the spin and valley quantum numbers. We analyze the zero-temperature magnetic instabilities of two-valley semiconductors with SOI, in-plane magnetic field, and electron-electron interaction. The interplay of an applied in-plane magnetic field and the SOI results in non-collinear spin quantization in different valleys. Together with the exchange intervalley interaction this results in a rich phase diagram containing four non-trivial magnetic phases. The negative non-analytic cubic correction to the free energy, which is always present in an interacting 2DEG, is responsible for first order phase transitions. Here, we show that non-zero ground state values of the order parameters can cut this cubic non-analyticity and drive certain magnetic phase transitions second order. We also find two tri-critical points at zero temperature which together with the line of second order phase transitions constitute the quantum critical sector of the phase diagram. The phase transitions can be tuned externally by electrostatic gates or by the in-plane magnetic field.