Valence State Energies Research Articles

Broadband La2LiSbO6: Cr3+ Phosphors with Double Luminescent Centers for NIR pc-LEDs.

The La2LiSbO6: xCr3+ phosphors were synthesized by means of a high-temperature solid-phase method. Based on the differences in ionic radius, valence state, and formation energy, the substitution sites of Cr3+ ions are discussed in detail. The optimized doping concentration of Cr3+ is determined to be 0.01. Under 517 nm excitation, the La2LiSbO6: 0.01Cr3+ phosphor presents a wide emission band (from 700 to 1350 nm) with a peak centered at 952 nm. Additionally, its corresponding full width at half-maximum is 155 nm, and the internal quantum efficiency reaches 62.4%. Meanwhile, the emission intensity of the La2LiSbO6: 0.01Cr3+ phosphor at 373 K is about 63.7% of that at room temperature, exhibiting good thermal stability. Aiming to fabricate a near-infrared phosphor-converted light-emitting diode device, the La2LiSbO6: 0.01Cr3+ phosphor is mixed with epoxy adhesive and cured on a green light-emitting diode chip. Under the irradiation of the fabricated light-emitting diode device, fruits and writing in the dark environment can be captured by a near-infrared camera. Hence, the La2LiSbO6: 0.01Cr3+ phosphor is promising for night vision.

High performance detection of ethanol based on HoFeO3 microsphere gas sensor

The HoFeO3 gas sensitive material was prepared by simple hydrothermal method and high temperature calcination. In this work, XRD, EDX, SEM, and TEM characterization methods were used to analyze the HoFeO3 crystal structure and morphology features. The chemical valence state and binding energy of HoFeO3 were analyzed by XPS. The slightly rough surface morphology and low binding energy Ho–O bond can promote the better binding reaction of reducing gas molecules with the material surface, which is beneficial to enhance the gas sensitivity properties of the material. The HoFeO3 gas-sensitive material sensor shows excellent selectivity for ethanol gas, with a response value of 33 and fast response recovery time 12 s/11 s. Tested at a broad range of ethanol gas concentrations, 90% excellent adsorption and desorption rates are achieved. In addition, we have analyzed the sensing mechanism of the HoFeO3 gas sensor.

A similarity transformed second-order approximate coupled cluster method for the excited states: Theory, implementation, and benchmark.

We present a novel and cost-effective approach of using a second similarity transformation of the Hamiltonian to include the missing higher-order terms in the second-order approximate coupled cluster singles and doubles (CC2) model. The performance of the newly developed ST-EOM-CC2 model has been investigated for the calculation of excitation energies of valence, Rydberg, and charge-transfer excited states. The method shows significant improvement in the excitation energies of Rydberg and charge-transfer excited states as compared to the conventional CC2 method while retaining the good performance of the latter for the valence excited state. This method retains the charge-transfer separability of the charge-transfer excited states, which is a significant advantage over the traditional CC2 method. A second order many-body perturbation theory variant of the new method is also proposed.

Research on the Mathematical Model of Local Equilibrium in the Top-Blown Smelting Process of Electronic Waste

In the present study, the local equilibrium modeling and division method of the multiphase non-equilibrium for the top-blowing smelting process of electronic waste was investigated based on the local equilibrium hypothesis. And the mathematical description of the multi-phase equilibrium of each local area and the correlation method between the local areas were studied by analysis of relationships among the valence state, phase, composition, and Gibbs free energy of each element. Afterward, the reaction characteristic data such as melting material, product phase, composition, temperature, atmosphere, etc. were obtained via industrial measurement experiments. Based on these, a mathematical model of local equilibrium for the top-blowing smelting process of electronic waste was established. Finally, the thermodynamic digital simulation system was developed via the calculation of metallurgical process and online control platform MetCal Desk (v7.00, MetCal, Ganzhou, China), which can investigate the element distribution behavior during the smelting process and provide theoretical guidance for the industrial production practice.

The vacuum ultraviolet absorption spectrum of norbornadiene: Vibrational analysis of the singlet and triplet valence states of norbornadiene by configuration interaction and density functional calculations.

A synchrotron-based vacuum ultraviolet (VUV) absorption spectrum of norbornadiene (NBD) is reported, and the extensive vibrational structure obtained has been analyzed. The previously known 5b13s-Rydberg state has been reinterpreted by comparison with our recent high-resolution photoelectron spectral analysis of the X2B1 ionic state. Additional vibrational details in the region of this Rydberg state are observed in its VUV spectrum when compared with the photoelectron 2B1 ionic state; this is attributed to the underlying valence state structure in the VUV. Valence and Rydberg state energies have been obtained by configuration interaction and time-dependent density functional theoretical methods. Several low-lying singlet valence states, especially those that arise from ππ* excitations, conventionally termed NV1 to NV4, have been examined in detail. Their Franck-Condon (FC) and Herzberg-Teller (HT) profiles have been investigated and fitted to the VUV spectrum. Estimates of the experimental 00 band positions have been made from these fits. The anomaly of the observed UV absorption by the 1A2 state of NBD is attributed to HT effects. Generally, the HT components are less than 10% of the FC terms. The calculated 5b13s lowest Rydberg state also shows a low level of HT components. The observed electron impact spectra of NBD have been analyzed in detail in terms of triplet states.

Theorems and rules connecting bond energy and bond order with electronegativity equalization and hardness maximization

Bond orders are attributed a new role in rationalizing the electronegativity equalization (ENE) and maximum hardness (MH) rules. The following rules and theorems are formulated for chemical species (atoms, groups, molecules), X, Y, XY, their ionization energies, I, electron affinities, A, electronegativity, χ = ½(I + A), and chemical hardness, η = ½ (I − A). Rule 1 Sanderson’s principle of electronegativity equalization is supported (individual deviations < 10%) by association reactions, X + Y → XY, if the ionic bond dissociation energies are equal, D (XY+) = D (XY−), or, equivalently, if the relative bond orders are equal, BOrel (XY+) = BOrel (XY−). Rule 2 Sanderson’s principle of electronegativity equalization is supported (individual deviations < 10%) by association reactions, X + Y → XY, if the formal bond orders, FBO, of the ions are equal, FBO (XY+) = FBO (XY−). Theorem 1 The electronegativity is not equalized by association reactions, X + Y → XY, if the formal bond orders of the ions differ, FBO (XY+) − FBO (XY−) ≠ 0. Theorem 2 The chemical hardness is increased by nonpolar bond formation, 2X → X2, if (and for atomic X: if and only if) the sum BOrel (X2+) + BOrel (X2−) < 2. Rule 3 The chemical hardness is decreased, thus the “maximum hardness principle” violated by association reactions, X + Y → XY, if (but not only if) BOrel (XY+) + BOrel (XY−) > 2. The theorems are proved, and the rules corroborated with the help of elementary thermochemical cycles according to the first law of thermodynamics. They place new conditions on the “structural principles” ENE and MH. The performances of different electronegativities and hardness scales are compared with respect to ENE and MH. The scales based on valence-state energies perform consistently better than scales based on ground-state energies. The present work provides the explanation for the order of magnitude better performance of valence-state ENE compared to that of the ground-state ENE. We here show by a new approach that the combination of several fuzzy concepts clarifies the situation and helps in defining the range of validity of rules and principles derived from such concepts.

Accuracy of Spin-Component-Scaled CC2 Excitation Energies and Potential Energy Surfaces.

Benchmark calculations with the Spin-Component-Scaled CC2 variants SCS-CC2 and SOS-CC2 are presented for the electronically excited valence and Rydberg states of small- and medium-sized molecules. Besides the vertical excitation energies and excited state gradients, the potential energy surfaces are also investigated via scans following the forces that act in the Franck-Condon region. The results are compared to the regular CC2 ones, as well as higher level methods CCSD, CCSD(T)(a)*, and CCSDT. The results indicate that a large fraction of the flaws of CC2 revealed by earlier studies disappears if spin-component scaling is employed. This makes these variants attractive alternatives of their unscaled counterparts, offering competitive accuracy of vertical excitation energies of both valence and Rydberg type states and reliable potential energy surfaces, while also maintaining a low-power-scaling computational cost with the system size.

The antibacterial stability of poly(dopamine) in-situ reduction and chelation nano-Ag based on bacterial cellulose network template

In recent years, continuous and stable antibacterial ability has received extensive attention in the field of antibacterial composite materials. The researchers expect a kind of antibacterial composites with continuous and stable antibacterial acting and good biocompatibility. Herein we used a unique in-situ modification methods which inspired self-polymerization of dopamine to fix the nano-Ag on the bacterial cellulose (BC). The antibacterial properties of composites were tested in two new methods (antibacterial stability and antibacterial durability). We researched the cause of the antibacterial properties by analyzing the valence state and binding energy of Ag. The chelation between PDA and Ag is considered to the key to stable release of Ag + . The three-dimensional network of BC is also thought to play some role in making Ag + release stability. Moreover, PDA as a reducing agent, reacting with Tollens reagent to produce nano-Ag nanoparticles, is a good method for reducing the toxicity of nano-Ag and enhancing the biological compatibility of composites. Our results hence illustrate that the BC antimicrobial composites by PDA in-situ reduction nano-Ag has a great potential as an antibacterial dressing with stable antimicrobial properties and biocompatibility. • PDA can reduce toxicity of nano-Ag and enhance biocompatibility of composites. • Antibacterial properties are tested in two methods called stability and durability. • The cause of antibacterial properties is researched by XPS and Ag + release curve.

Electronic structure of lanthanide scandates

X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and density functional theory calculations were used to study the electronic structure of three lanthanide scandates: GdScO3, TbScO3, and DyScO3. X-ray photoelectron spectra simulated from first principles calculations using a combination of on-site hybrid and GGA+U methods were found to be in good agreement with experimental x-ray photoelectron spectra. The hybrid method was used to model the ground state electronic structure and the GGA+U method accounted for the shift of valence state energies due to photoelectron emission via a Slater-Janak transition state approach. From these results, the lanthanide scandate valence bands were determined to be composed of Ln4f, O2p, and Sc3d states, in agreement with previous work. However, contrary to previous work the minority Ln4f states were found to be located closer to, and in some cases at, the valence band maximum. This suggests that minority Ln4f electrons may play a larger role in lanthanide scandate properties than previously thought.

Accuracy of Coupled Cluster Excitation Energies in Diffuse Basis Sets.

We present a comprehensive statistical analysis on the accuracy of various excited state Coupled Cluster methods, accentuating the effect of diffuse basis sets on vertical excitation energies of valence and Rydberg-type states. Many popular approximate doubles and triples methods are benchmarked with basis sets up to aug-cc-pVTZ, with high level EOM-CCSDT results used as reference. The results reveal a serious deficiency of CC2 linear response and CIS(D) techniques in the description of Rydberg states, a feature not shown by the EOM-CCSD(2) and EOM-CCSD variants. The CC3 theory proves to be an accurate choice among the iterative approximate triples methods, while the novel perturbation-based CCSD(T)(a)* variant turns out to be the best way to include the effect of triple excitations in a noniterative way.

Investigation of the Impact of Different Terms in the Second Order Hamiltonian on Excitation Energies of Valence and Rydberg States.

Describing electronically excited states of molecules accurately poses a challenging problem for theoretical methods. Popular second order techniques like Linear Response CC2 (CC2-LR), Partitioned Equation-of-Motion MBPT(2) (P-EOM-MBPT(2)), or Equation-of-Motion CCSD(2) (EOM-CCSD(2)) often produce results that are controversial and are ill-balanced with their accuracy on valence and Rydberg type states. In this study, we connect the theory of these methods and, to investigate the origin of their different behavior, establish a series of intermediate variants. The accuracy of these on excitation energies of singlet valence and Rydberg electronic states is benchmarked on a large sample against high-accuracy Linear Response CC3 references. The results reveal the role of individual terms of the second order similarity transformed Hamiltonian, and the reason for the bad performance of CC2-LR in the description of Rydberg states. We also clarify the importance of the T̂1 transformation employed in the CC2 procedure, which is found to be very small for vertical excitation energies.

Excited states of OH-(H₂O)n clusters for n = 1-4: an ab initio study.

Equation of motion coupled cluster calculations were performed on various structures of OH in clusters with one, two, three, and four water molecules to determine the energies of valence and charge transfer states. Motivation for these calculations is to understand the absorption spectrum of OH in water. Previous calculations on these species have confirmed that the longer wavelength transition observed is due to the A((2)∑) ← X((2)∏) valence transition, while the shorter wavelength transition is due to a charge-transfer from H2O to OH. While these previous calculations identified the lowest energy charge-transfer state, our calculations have included sufficient states to identify additional solvent-to-solute charge transfer states. The minimum energy structures of the clusters were determined by application of the Monte Carlo technique to identify candidate cluster structures, followed by optimization at the level of second-order Møller-Plesset perturbation theory. Calculations were performed on two structures of OH-H2O, three structures of OH-(H2O)2, four structures of OH-(H2O)3, and seven structures of OH-(H2O)4. Confirming previous calculations, as the number of water molecules increases, the energies of the excited valence and charge-transfer states decrease; however, the total number of charge-transfer states increases with the number of water molecules, suggesting that in the limit of OH in liquid water, the charge-transfer states form a band.

Testing time-dependent density functional theory with depopulated molecular orbitals for predicting electronic excitation energies of valence, Rydberg, and charge-transfer states and potential energies near a conical intersection.

Kohn-Sham (KS) time-dependent density functional theory (TDDFT) with most exchange-correlation functionals is well known to systematically underestimate the excitation energies of Rydberg and charge-transfer excited states of atomic and molecular systems. To improve the description of Rydberg states within the KS TDDFT framework, Gaiduk et al. [Phys. Rev. Lett. 108, 253005 (2012)] proposed a scheme that may be called HOMO depopulation. In this study, we tested this scheme on an extensive dataset of valence and Rydberg excitation energies of various atoms, ions, and molecules. It is also tested on a charge-transfer excitation of NH3-F2 and on the potential energy curves of NH3 near a conical intersection. We found that the method can indeed significantly improve the accuracy of predicted Rydberg excitation energies while preserving reasonable accuracy for valence excitation energies. However, it does not appear to improve the description of charge-transfer excitations that are severely underestimated by standard KS TDDFT with conventional exchange-correlation functionals, nor does it perform appreciably better than standard TDDFT for the calculation of potential energy surfaces.

Analytical energy gradients for second-order multireference perturbation theory using density fitting

We present algorithms for computing analytical energy gradients for multi-configuration self-consistent field methods and partially internally contracted complete active space second-order perturbation theory (CASPT2) using density fitting (DF). Our implementation is applicable to both single-state and multi-state CASPT2 analytical gradients. The accuracy of the new methods is demonstrated for structures and excitation energies of valence and Rydberg states of pyrrole, as well as for structures and adiabatic singlet-triplet energy splittings for the hydro-, the O,O(')-formato-, and the N,N(')-diiminato-copper-dioxygen complexes. It is shown that the effects of density fitting on optimized structures and relative energies are negligible. For cases in which the total cost is dominated by the integral evaluations and transformations, the DF-CASPT2 gradient calculations are found to be faster than the corresponding conventional calculations by typically a factor of three to five using triple-ζ basis sets, and by about a factor of ten using quadruple-ζ basis sets.

Photo-Absorption Studies on Formaldehyde Using Synchrotron Radiation at Indus I

ABSTRACT Photo-absorption spectra of formaldehyde (HCHO) is recorded in the range of 6–11.5 eV at various pressures (<0.001–2 mbar) at an average resolution of 1.2 Å using Photophysics beam line at the 450 MeV Indus-1 synchrotron radiation facilities at RRCAT Indore, India. The spectrum is found to consist exclusively of n → Rydberg transitions converging to the ground state of HCHO+. The highest identified Rydberg states, observed up to the first ionization limit of HCHO, correspond to 7s, 11p, 9d, and 12f orbitals. Analyzed electronic spectrum along with the intensities and quantum defects are presented. To interpret the observed weak valence transitions instead of strong valence transitions, a theoretical study of Rydberg and valence electronic states of HCHO is performed in the framework of single configuration interaction (CIS) and time-dependent density functional theory (TDDFT) using different basis sets. Electronic transition energies of high-lying singlet and triplet valence states as calculated using TDDFT (B3LYP) level of theory are found to give fairly-good agreement with the experimental data.

Ab Initio Study of the VUV-Induced Multistate Photodynamics of Formaldehyde

Although formaldehyde, H₂CO, has been extensively studied there are still several issues not-well understood, specially regarding its dynamics in the VUV energy range, mainly due to the amount of nonadiabatic effects governing its dynamics. Most of the theoretical work on this molecule has focused on vertical excitation energies of Rydberg and valence states. In contrast to photodissociation processes involving the lowest-lying electronic states below 4.0 eV, there is little known about the photodynamics of the high-lying electronic states of formaldehyde (7-10 eV). One question of particular interest is why the (π, π*) electronic state is invisible experimentally even though it corresponds to a strongly dipole-allowed transition. In this work we present a coupled multisurface 2D photodynamics study of formaldehyde along the CO stretching and the symmetric HCH bending motion, using a quantum time-dependent approach. Potential energy curves along all the vibrational normal modes of formaldehyde have been computed using equation-of-motion coupled cluster including single and double excitations with a quadruply augmented basis set. In the case of the CO stretching coordinate, state-averaged complete active space self-consistent field followed by multireference configuration interaction was used for large values of this coordinate. 2D (for the CO stretching coordinate and the HCH angle) and 3D (including the out-of-plane distortion) potential energy surfaces have been computed for several Rydberg and valence states. Several conical intersections (crossings between potential energy surfaces of the same multiplicity) have been characterized and analyzed and a 2D 5 × 5 diabatic model Hamiltonian has been constructed. Based on this Hamiltonian, electronic absorption spectra, adiabatic and diabatic electronic populations and vibrational densities have been obtained and analyzed. The experimental VUV absorption spectrum in the 7-10 eV energy range is well reproduced, including the vibrational structure and the high irregularity in the regime of strong interaction between the (π, π*) electronic state and neighboring Rydberg states.

ChemInform Abstract: Chemical Clusters from Solid State Systems at High Temperatures. Interstitials as a Means to Stability and Versatility

The reactivity of many naked clusters and the means by which these may be isolated as stable chemical clusters are briefly considered for the orbitally-rich transition metals, where clusters must be sequestered by coordination with ligands, and for the heavier main group elements that utilize only t hree p orbitals in bonding. shell configurations a re known for the latter group both as solids at room temperature and in cluster beams. at elevated temperatures are o btained with chloride, sulfide, etc. as ligands. Greater versatility and variety have recently been found for electron-precise clusters that require an interstitial atom Z within M6X12-type clusters for stability, as with the Ai(Zr6(Z)XI2)X, family and rare-earth-eleme nt analogs where 22 different examples of Z and many structure types are known for X = C1, Br, I. A newer and even broader area of cluster chemistry involves interstitials bonded within chains of confacial octahedra in a variety of polar intermetallic phases that occur in the Mn5Si3 structure (-&(Mn3Si3-Mn2)), where the l arge differences in valence state energies of the component atoms generally assure that valence bonding levels on the main-group element are filled first. The electron-rich Zr5Sb3 host is found to form Zr5Sb3Z phases with at least 16 examples of Z. calculational results for the binary host and for the sulfide are considered. Examples of similar investigations are described for the Zr5Sn3, Zr5Pb3, La5Ge3, La5Pb3, and M&, M = Ca, Sr or Ba and 6 = Sb or Bi.

Sodium and potassium monolayers on Be(0001) investigated by photoemission and electronic structure calculations

Photoemission spectra show that Be(0001) surface states shift to lower energy with increasing Na or K coverage in the monolayer range. At an intermediate monolayer coverage a quantum well state appears near the Fermi edge and shifts to lower energy reaching saturation energy at full monolayer coverage. At full monolayer coverage low energy electron diffraction shows $2\ifmmode\times\else\texttimes\fi{}2$ order for K while Na forms an incommensurate close-packed structure aligned with the substrate. As a result of the different structures, the photoemission spectra show qualitative differences that are explained by diffraction. First-principles calculations for Be(0001) and $p(2\ifmmode\times\else\texttimes\fi{}2)\text{K}/\text{Be}(0001)$ reproduce reasonably the measured energy shifts and dispersions. Spectra recorded for the shallow alkali-metal core levels show that the adlayer is inhomogeneous in an intermediate coverage range. While this is not noted when the valence state energies are measured a linewidth change observed for one of the surface states is ascribed to this inhomogeneity. It is suggested that the onset of inhomogeneity is associated with the occupation of states in the quantum well band. Occupation of these states, which are highly localized to the adlayer, gives metal character to the layer over an increasing area as the coverage is increased making the film homogeneous at high monolayer coverage. An anomalous emission line is observed for both Na and K as a low energy companion to the quantum well state line becoming increasingly separated from this as the coverage increases. We suggest that the satellite is due to an energy loss associated with collective oscillations in the overlayer.

An extended multireference study of the electronic states of para-benzyne

A state-averaged, multireference complete active space (CAS) approach was used for the determination of the vertical excitation energies of valence and Rydberg states of para-benzyne. Orbitals were generated with a 10- and 32-state averaged multiconfigurational self-consistent field approach. Electron correlation was included using multireference configuration interaction with singles and doubles, including the Pople correction for size extensivity, multireference averaged quadratic coupled cluster (MR-AQCC), and MR-AQCC based on linear response theory. There is a very high density of electronic states in this diradical system-there are more than 17 states within 7 eV of the ground state including two 3s Rydberg states. All excitations, except 2 (1)A(g), are from the pi system to the sigmasigma(*) system. Of the 32 states characterized, 15 were multiconfigurational, including the ground (1)A(g) state, providing further evidence for the necessity of a multireference approach for p-benzyne. The vertical singlet-triplet splitting was also characterized using a two-state averaged approach. A CAS(2,2) calculation was shown to be inadequate due to interaction with the pi orbitals.

Ab initio R-matrix/multichannel quantum defecttheory study of nitric oxide

Ab initio R-matrix techniques are combined withmulti-channel quantum defect theory to determine theproperties of arbitrarily highly excited electronic states ofnitric oxide. Results are obtained for l = 0-4 channelsassociated with the four lowest NO+ target channels, namely1Σ+, 3Σ+, 3Π and3Δ. Energy and bond length variations of the quantumdefect functions for all target states are reported. Certainsmall surface amplitude R-matrix poles also serve to determinethe energies of valence states. Diabatic potential curves forRydberg states converging to the 1Σ+ and3Σ+ target states and for the valence states arepresented. Systematic jumps in the pσ quantum defectsfor all target states as the bond length increases beyondR = 2.5 au are attributed to Rydbergization of the antibonding2pσ* molecular orbital.