Energies Of Electronic States Research Articles

Towards Near-Exact Solutions of Molecular Electronic Structure: Full Coupled-Cluster Reduction with a Second-Order Perturbative Correction.

We introduce a new augmented adaptation of the recently developed full coupled-cluster reduction (FCCR) with a second-order perturbative correction, abbreviated as FCCR(2). FCCR is a selected coupled-cluster expansion aimed at optimally reducing the excitation manifold and commutator expansions for high-rank excitations for obtaining accurate solutions of the electronic Schödinger equation in a size-extensive manner. The present FCCR(2) enables estimating the residual correlation of FCCR by the second-order perturbative correction E(2) from the complementary space of the FCCR projection manifold. The linear relationship between E(2) and the energy of FCCR(2) allows accurate estimates of near-exact energies for a wide variety of molecules with strong electron correlation. The potential of the method is demonstrated using challenging cases, the ground-state electronic energy of the benzene molecule in equilibrium and stretched geometries, and the isomerization energy of the transition metal complex [Cu(NH3)]2O22+.

The performance of CIPSI on the ground state electronic energy of benzene

Following the recent work of Eriksen et al. [J. Phys. Chem. Lett. 11, 8922 (2020)], we report the performance of the configuration interaction using a perturbative selection made iteratively method on the non-relativistic frozen-core correlation energy of the benzene molecule in the cc-pVDZ basis. Following our usual protocol, we obtain a correlation energy of -863.4 mEh, which agrees with the theoretical estimate of -863 mEh proposed by Eriksen et al. [J. Phys. Chem. Lett. 11, 8922 (2020)] using an extensive array of highly accurate new electronic structure methods.

Multidimensional QSPR Model for Calculating the Critical Pressure of Substituted Naphthalenes in First-Order Phase Transitions

A multivariate QSPR model is proposed for predicting the critical pressure of substituted naphthalenes through combinations of topological molecular graph descriptors. Fifty-nine naphthalene derivatives are examined that are randomly divided into base and test sets. In considering naphthalene molecules, it was assumed the critical pressure is determined by descriptors that characterize the branching of the structure (the Wiener index) and the Huckel spectrum, which considers only the interaction between neighboring atoms (functions of the eigenvalues of the topological matrix). The energy of intermolecular interactions depends largely on the specific size of the molecules and their degree of branching. Multiple bonds are considered in calculating the Wiener index. The sum of the squares of the eigenvalues of the topological matrix describes deviations of the Huckel energy of electronic states from its average value in a molecule. The choice of the squares of the eigenvalues of the molecular graph is due to a consequence of the Horst Sachs theorem. The descriptors used in this work are calculated using the Maple 13 and PascalABCNet software. To verify the prognostic capabilities of the proposed model, critical pressures were calculated for compounds not included in the base series. The QSPR model adequately describes the critical pressure of naphthalenes in liquid–vapor phase transitions, as is confirmed by experimental data and statistical data processing. The results can be recommended for estimating the critical pressure of known and newly synthesized naphthalenes, and used in scientific and engineering calculations in petrochemistry and supercritical fluid technology.

The Ground State Electronic Energy of Benzene.

We report on the findings of a blind challenge devoted to determining the frozen-core, full configuration interaction (FCI) ground-state energy of the benzene molecule in a standard correlation-consistent basis set of double-ζ quality. As a broad international endeavor, our suite of wave function-based correlation methods collectively represents a diverse view of the high-accuracy repertoire offered by modern electronic structure theory. In our assessment, the evaluated high-level methods are all found to qualitatively agree on a final correlation energy, with most methods yielding an estimate of the FCI value around -863 mEH. However, we find the root-mean-square deviation of the energies from the studied methods to be considerable (1.3 mEH), which in light of the acclaimed performance of each of the methods for smaller molecular systems clearly displays the challenges faced in extending reliable, near-exact correlation methods to larger systems. While the discrepancies exposed by our study thus emphasize the fact that the current state-of-the-art approaches leave room for improvement, we still expect the present assessment to provide a valuable community resource for benchmark and calibration purposes going forward.

The performance of phaseless auxiliary-field quantum Monte Carlo on the ground state electronic energy of benzene.

The ground state electronic energy of benzene is the focus of a recent blind test by Eriksen and co-workers [arXiv:2008.02678]. In this note, we report the phaseless auxiliary-field quantum Monte Carlo (ph-AFQMC) results on the identical problem. We examine trial wavefunctions of the spin-restricted Hartree-Fock (RHF), and complete active space self-consistent field (CASSCF) with an active space of 6-electron and 6-orbital (i.e., CAS(6,6)) form for the cc-pVDZ basis set. ph-AFQMC+RHF deviates from the value where many methods agreed on (i.e., -863 m$E_h$) by -3.1(3) m$E_h$ whereas ph-AFQMC+CAS(6,6) deviates from the same value by -1.3(4) m$E_h$. In addition to this, we report the frozen core correlation energy of ph-AFQMC+RHF in the cc-pVTZ and cc-pVQZ basis sets as well as their complete basis set limit. Our findings highlight the accuracy, flexibility, and scalability of ph-AFQMC with simple trial wavefunctions.

Switching Competition between Electron and Energy Transfers in Porphyrin-Fullerene Dyads.

Porphyrin-fullerene dyads were intensively studied as molecular donor-acceptor systems providing efficient photoinduced charge separation (CS). A practical advantage of the dyads is the possibility to tune its CS process by the porphyrin periphery modification, which allows one to optimize the dyad for particular applications. However, this tuning process is typically composed of a series of trial stages involving the development of complex synthetic schemes. To address the issue, we synthesized a series of dyads with properties switching between electron and energy transfer in both polar (benzonitrile) and nonpolar (toluene) media and developed a computation procedure with sufficient reliability by which we can predict the CS properties of the dyad in different media and design new dyads. The dyads photochemistry was established by conducting ultrafast transient absorption studies in toluene, anisole, and benzonitrile. The most crucial step in computational modeling was to establish a procedure for correction of the electronic-state energies obtained by DFT so that the effects of the electron correlation and the long-range interactions are properly incorporated. We also carried out standard electrochemical measurements and show that our computation approach predicts better thermodynamics of the dyads in different solvents.

Electronic States in a Doubly Eccentric Cylindrical Quantum Wire

Electronic states of a single electron in doubly eccentric cylindrical quantum wire are theoretically investigated in this paper. The motion of electron in quantum wire is free along axial direction in a cylindrical quantum wire and restricted in annular regions by three different parallel finite cylindrical barriers as soft wall confinement. The effective mass Schrödinger equation with effective mass boundary conditions is used to find energy eigenvalues and corresponding wavefunctions. Addition theorem for cylindrical Bessel functions is used to shift the origin for applying boundary conditions at different circular boundaries. Fourier expansion is applied after addition theorem to get wavefunctions in analytical form. A determinant equation is obtained as a result of applications of effective mass boundary conditions which roots gives energy of various electronic states. The lowest root gives ground state energy. The variation in ground state energy with eccentricity is obtained numerically and presented graphically. Electronic states in massive wall confinement and hard wall confinement is further obtained as limiting behavior of the states obtained in soft wall confinement. The knowledge of electronic states in such cylindrical hetrostructures semiconductor material can lead to improve the efficiency of many quantum devices.

Coming to Terms with Term States

In multielectron atoms or molecules, quantized electronic energy states known as term states provide a framework for interpreting absorption and emission spectra. Enumerating the term states associ...

Investigation of quantum confinement phenomenon in composition- and diameter-modulated nanowires

The effects of diameter variation as a result of composition modulation along a nanowire on the confined energy states of electrons have been investigated theoretically. Possible confined states have been predicted by examining an effective potential term. Our results indicate that for a given radius of the wire, there exists a critical radius for modulation part below which carriers could not bound to the modulated part. The critical radius increases and reaches a limiting value as wire radius increases, specifying that the bound states could survive even when the radius of modulation decreases below the radius of remaining wire. Also, application of magnetic field could affect the critical radius so that the confinements to the modulated part are suppressed gradually by increasing the field strength, which is a sign of type-I to type-II transitions. Examination of results by the numerically solving the Schrodinger equation confirms the analytical predictions.

Upconversion properties of Gd-based ceramics, attached into polystyrene films

Tm3+- and Yb3+-doped lithium-gadolinium oxide (Li-Gd2O3) ceramics, prepared by the simple evaporation technique, were incorporated into polystyrene (PS) films (as recycled Styrofoam). A study of the upconversion (UC) emission from Tm3+ as well as Yb3+ ions was performed under continuous wave excitation of a 980-nm laser, for both powder and PS film samples. High-intensity light emissions (UC) were observed at 476, 488, and 665 nm, associated with inter electronic energy state transitions of the Tm3+ ion, from 1D2 to 3F4, 1G4 to 3H6, and 3F3 to 3H6, respectively. Yb3+ presence makes possible the thulium blue emission in the UC luminescence because it acts as a sensitizer under 980-nm excitation. Lithium is used as part of the host lattice (Lix-Gd2-xO3; 0 ≤ x ≥ 1) in order to achieve a greater crystallinity as Li+ acts as fluxing agent. The PS films remain highly transparent in the light’s visible region even after the incorporation of the ceramic particles (around 80% T).

Genetic Algorithm for quick finding of diatomic molecule potential parameters

ABSTRACT Application of Genetic Algorithm (GA) for determination of parameters of an analytical representation of diatomic molecule potential is presented. GA can be used for finding potential characteristics of an electronic energy state which can be described by an analytical function. GA was tested on two artificially generated datasets which base on potentials with known characteristics and two laser induced fluorescence excitation spectra recorded using transitions in CdKr and CdAr molecules. Tests on generated datasets showed that GA can properly reproduce parameters of the potentials. Tests on experimental spectra indicated that changing the potential model from a Morse, which is frequently used as a starting potential in the inverse perturbation approach method, to an expanded Morse oscillator leads to noticeable improvement of agreement between simulated and experimental data.

Fine Spin-Dependent Splitting of Electronic Excitations and Their Dispersion in Single-Layer Graphene and Graphite

The dispersion dependences of electronic excitations in single-layer graphene and crystalline graphite have been studied taking the electron spin into consideration. Compatibility conditions for two-valued irreducible projective representations characterizing the symmetry of spinor excitations in the above structures and the distributions of spinor quantum states over projective classes and irreducible projective representations at all high-symmetry points in the corresponding Brillouin zones are determined for the first time. The principal existence of the spin-dependent splitting (or merging) of the electronic energy states, in particular, the electronic п-bands at the Dirac points, is established. The magnitude of spin-dependent splitting can be significant, e.g., for the transition-metal chalcogenides belonging to the same spatial symmetry group as crystalline graphite. However, because of the weak spin-orbit interaction for carbon atoms, it turns out small for all carbon structures including single-layer graphene and crystalline graphite.

Bound→free and bound→bound multichannel emission spectra from selectively excited Rydberg states in the ZnAr and CdAr van der Waals complexes

Multichannel dispersed emission spectra originated upon a selective excitation of Rydberg electronic energy states in the ZnAr and CdAr van der Waals (vdW) complexes are simulated and analysed as a proof-of-concept of the future experimental approach. Simulations of the emission spectra are based on ab-initio calculated interatomic potentials and transition dipole moments (TDMs), that for ZnAr were newly calculated. Experimental set-up that is under construction along with the experimental procedure are discussed.

Photoelectrochemical and photocatalytic detoxification of Cr(VI) to Cr(III) over terpyridine-derivatized Au nanoparticles on carbon paper and indium-tin-oxide electrodes

Detoxification of hexavalent chromium (Cr(VI)) in the environment and development of corresponding new materials and detoxification protocols have actively been studied and applied. Herein, 2,2′:6′,2′'-terpyridine-4′-thiol (STpy) was functionalized on Au nanoparticle (NP)-loaded carbon paper (CP) and indium-tin-oxide (ITO) electrodes (CP-AuNP and ITO-AuNP, respectively), and the photoelectrochemical (PEC) and photocatalytic detoxification of Cr(VI) using the resulting electrodes was investigated by cyclic voltammetry. Density functional theory at the B3LYP/6-31G level was used for geometry optimization, and the electronic energy state calculation was conducted at the TD-SCF/DFT/B3LYP level. For bare CP, ITO, and STpy-modified AuNP electrodes, the reduction potentials of Cr(VI) were around + 0.3, −0.2 V, and + 0.5 V (vs. Ag/AgCl), respectively. The PEC and photocatalytic Cr(VI) reduction performance of CP-AuNP was significantly improved upon STpy functionalization. Thus, these newly developed functionalized systems can provide very useful information for further improving the detoxification performances for various hazardous metals.

Lanthanide (III) ions as multichannel acceptors for bimolecular photoinduced electron transfer reactions with coumarin dyes

Understanding the kinetics and energetics of photoinduced electron transfer (PET) reactions is of considerable research interest in photochemical sciences. In this study, interactions between trivalent lanthanide ions (Ln(III)) as electron acceptors and coumarin dyes as electron donors have been investigated in aqueous media using ground state absorption, steady-state (SS) emission, time-resolved (TR) fluorescence and laser flash photolysis (LFP) techniques. Among different Ln(III) ions, only Eu(III), Yb(III) and Sm(III) are found to display substantial interaction with the excited singlet (S1) state of the coumarin dyes, which correspond well with the favorable free energy changes (negative ΔG0) associated with the PET reactions in these coumarin-Ln(III) systems. For other Ln(III) ions, as ΔG0 is not favorable, they do not show any interaction with the excited coumarin dyes. Among the interacting coumarin-Ln(III) systems, bimolecular quenching rate constant (kq) increases consistently with the increasing exergonicity (−ΔG0), when each of the Ln(III) ions are considered independently, except for Eu(III), for which the kq values have already reached the diffusion controlled limit. However, considering all the Ln(III) ions together, the kq values do not show any common correlation with the changing ΔG0 values. The kq values are in general much lower for Yb(III) quencher as compared to Sm(III), even though the exergonicity values for coumarin-Yb(III) systems are more favorable than the coumarin-Sm(III) systems. Correlating the observed results based on the diffusion mediated bimolecular reaction model, we infer that depending on the ΔG0 values, some Ln(III) quenchers possibly also engage their upper electronic energy states as well to assist multichannel ET with the excited coumarin donors, and thereby modulating the kq values very substantially for different coumarin-Ln(III) systems. Apparently, the involvement of multichannel ET causes the total reorganization energy (λ) for ET reactions to differ largely for different Ln(III) ions, which would otherwise be very similar for all the coumarin-Ln(III) pairs. Observed results suggest that the intramolecular reorganization energy (λi) associated with lower electronic states of the hydrated Ln(III) ions is much larger than that associated with higher electronic states of these ions. While the involvement of multichannel ET is itself an intriguing inference, modulation in the ET kinetics and total λ values for different Ln(III) quenchers through the differential participation of the multichannel PET is also expected to find potential uses in the controlled utilization of such PET reactions in many practical areas.

Synergistic engineering of MoS2 via dual-metal doping strategy towards hydrogen evolution reaction

Molybdenum disulfide (MoS2) is reckoned as one of the most positive low-cost HER catalysts to replace platinum-based precious metals in acid media. Unfortunately, some issues preclude MoS2 from being truly applicable including limited active sites, poor conductivity and lack of intrinsic activity. Herein, we report a Cu, Pd co-doped MoS2 nanomaterial as an efficient and stable HER electrocatalysts, which partially resolve the above-mentioned problems and leads to high overall performance. Specifically, we improve the electric conductivity of the MoS2 by Cu dopant and realize the phase transition of MoS2 from pristine 2H phase to stable 1T phase by Pd dopant. More importantly, we increase active site density to facilitate fast electrocatalytic Faradaic process via synergistic effects of Cu and Pd doping, and tune electronic energy states of MoS2 to improve HER intrinsic activity. In acidic media, the performance of Cu-Pd-MoS2 catalyst in terms of a low overpotential (−93 mV) at 10 mA cm−2, a small Tafel slope of 77 mV dec−1, and an excellent stability is better than that of single-doped catalysts.

Designing Triphenylamine‐Configured Donor Materials with Promising Photovoltaic Properties for Highly Efficient Organic Solar Cells

AbstractThe increasing demand for energy expedited the development of efficient photovoltaic materials. Herein, four triphenylamine based push pull donor materials (D1‐D4) have been designed. The optical, electronic, photophysical properties and excited state energy of D1‐D4 have been investigated theoretically through DFT calculations at B3LYP/6‐31G (d,p) level of theory and compared with reference molecule R. The theoretical study of the designed molecules (D1‐D4) and reference molecule R with TD−B3LYP/6‐31G (d,p) level of theory was carried out both in gaseous and solvent (Chloroform/CPCM) phase to investigate their excited state properties. All the designed molecules D1‐D4 exhibited broad and intense absorption peaks in the visible spectrum from 300 nm to 450 nm range with narrow HOMO‐LUMO energy gaps as compared to reference R. The dipole moment of designed molecules D1‐D4 are higher than reference molecule R in both gas and solvent phase which may help to enhance the photovoltaic stability of organic solar cells devices. The open‐circuit voltages of designed molecules, D1‐D4 and the reference molecule R compared to PCBM are 0.71 V, 0.66 V, 0.54 V, 0.63 V, and 0.63 V, respectively. The % ETC for designed molecules insolvent as well as in the gas phase is lower than the reference molecule R which enables them to excite rapidly both in gas and solvent phase respectively. The hole and electron transfer mobilities values indicate that the designed molecules have a better electron and hole transport mobility values as compared to reference molecule R. Furthermore, conceptualized molecules are better and thus are recommended to experimentalists for out‐looking future developments of solar cells.

Investigation of electrochemical properties of various transition metals doped SnO2 spherical nanostructures for supercapacitor applications

Abstract A simple co-precipitation method has been used to synthesis SnO2 and different transition metal (Fe, Cu and Zn) doped SnO2 spherical nanostructures. The influence of doping concentration on the structural, optical, functional and morphological properties were carefully analysed by using X-ray diffraction, Fourier Transform Infrared Spectroscopy, UV–Visible spectroscopy and Scanning Electron Microscopy studies. The XRD pattern declared the formation of cassiterite rutile SnO2 with tetragonal structure. No impurity peaks correspond to the transition metal dopant was observed in the doped SnO2 samples. The average crystallite size was found to be 27.2, 24.1, 22.3 and 21.8 nm for pure and Fe, Cu and Zn-doped samples, respectively. The EDX spectra and element mapping assessed the presence of Sn, O, Fe, Cu and Zn species. The SEM images showed the spherical morphology for the synthesized pure and TM-doped samples. X-ray photoelectron spectra confirmed the electronic state and binding energy of the Sn, Cu, Zn, Fe and O. The electrochemical performance of the prepared electrodes were evaluated by galvanostatic charge-discharge, cyclic voltammetry and electrochemical impedance spectroscopy. The nanostructured Fe doped SnO2 electrode revealed a favorable specific capacitance of 270 F/g at a current density of 0.5 A/g and also it has excellent cycling stability of 98% retention over 2000 charging discharging cycles.

Boosting Catalysis of Pd Nanoparticles in MOFs by Pore Wall Engineering: The Roles of Electron Transfer and Adsorption Energy.

The chemical environment of metal nanoparticles (NPs) possesses significant influence on their catalytic performance yet is far from being well understood. Herein, tiny Pd NPs are encapsulated into the pore space of metal-organic frameworks (MOFs), UiO-66-X (X = H, OMe, NH2 , 2OH, 2OH(Hf)), affording Pd@UiO-66-X composites. The surface microenvironment of the Pd NPs is readily modulated by pore wall engineering, via the functional group and metal substitution in the MOFs. Consequently, the catalytic activity of Pd@UiO-66-X follows the order of Pd@UiO-66-OH > Pd@UiO-66-2OH(Hf) > Pd@UiO-66-NH2 > Pd@UiO-66-OMe > Pd@UiO-66-H toward the hydrogenation of benzoic acid. It is found that the activity difference is not only ascribed to the distinct charge transfer between Pd and the MOF, but is also explained by the discriminated substrate adsorption energy of Pd@UiO-66-X (-OH < -2OH(Hf) < -NH2 < -OMe < -H), based on CO-diffuse reflectance infrared Fourier transform spectra and density-functional theory (DFT) calculations. The Pd@UiO-66-OH, featuring a high Pd electronic state and moderate adsorption energy, displays the highest activity. This work highlights the influence of the surface microenvironment of guest metal NPs, the catalytic activity of which is dominated by electron transfer and the adsorption energy, via the systematic substitution of metal and functional groups in host MOFs.

What is the Bond Dissociation Energy of the Vanadium Hydride Cation?

Recent electronic state-selected measurements of the reactions of atomic vanadium cations with D2 and CO2 are reanalyzed to properly account for the kinetic energy distribution of the reactant neutrals. The need for this is demonstrated in the present work by comparing the D2 data to that obtained previously in earlier experiments but unpublished. It is shown that the earlier data, which utilized a surface ionization source of V+, and the state-selected data for V+(a5D2) are essentially identical in the threshold regions where they overlap. Differences in the electronic state energies and kinetic energy distributions of V+ in the two experiments are very small and much smaller than the kinetic energy distribution of the neutral reactant, which is identical in both experiments. It is shown that properly accounting for the latter distribution alters the conclusions regarding the threshold energy for the endothermic formation of VD+ such that recent conclusions regarding the bond energy of VD+ are substantially altered and found to reproduce the original bond energy determination. Accounting for all experiments, a revised best value for D0(VH+) is 2.07 ± 0.09 eV [or D0(VD+) = 2.10 ± 0.09 eV]. This conclusion is validated by high-level ab initio calculations. Differences in the new and older data sets for the V+ + D2 reaction at higher energies (above the onset for dissociation of the product ion) are also discussed. The same methodology is then applied to recent studies on the state-selected V+ + CO2 reaction.