Chemical binding and electron correlation in diatomic molecules as described by the FORS model and the FORS-IACC model

Using the model of the Full Optimized Reaction Space including the Intra-Atomic Correlation Correction, binding energies and other electronic properties have been calculated for several states of a number of diatomic molecules. In most cases this theoretical approach yields results agreeing with experimental values to within 0.2 eV. The investigation covers the molecules BH, CH, NH, OH, FH, N₂, O₂, F₂.     

Ab initio calculations on low-lying electronic states of PdH

Potential energy curves for the low-lying electronic states of PdH have been calculated using the MRCI method with scalar relativistic and spin-orbit corrections, and all electronic states correlating to the 4d¹⁰ (¹S), 4d⁹ 5s¹ (³D), 4d⁹ 5s¹ (¹D) and 4d⁸ 5s² (³F) states of Pd were included. Potential energy curves for the individual Ω states have been obtained, and the experimentally observed spectra of both PdH and PdD isotopologues have been assigned appropriately based on the ab initio results. Einstein A coefficients were calculated for other possible transitions from the low-lying electronic states to the X²Σ⁺ ground state. Diagonal and off-diagonal matrix elements of the spin-orbit Hamiltonian were calculated for all vibrational levels of the X²Σ⁺, 1²Δ, 1²Π, 2²Σ⁺ and 3²Σ⁺ states, and it was found from the eigenvectors that the vibrational wavefunctions of the 1²Δ_3/2 and 1²Π_3/2 states are mixed significantly in both PdH and PdD isotopologues.     

Intruder state avoidance multireference Møller-Plesset perturbation theory

A new perturbation approach is proposed that enhances the low‐order, perturbative convergence by modifying the zeroth‐order Hamiltonian in a manner that enlarges any small‐energy denominators that may otherwise appear in the perturbative expansion. This intruder state avoidance (ISA) method can be used in conjunction with any perturbative approach, but is most applicable to cases where small energy denominators arise from orthogonal‐space states—so‐called intruder states—that should, under normal circumstances, make a negligible contribution to the target state of interests. This ISA method is used with multireference Møller–Plesset (MRMP) perturbation theory on potential energy curves that are otherwise plagued by singularities when treated with (conventional) MRMP; calculation are performed on the 1³Σ state of O₂; and the 2¹Δ, 3¹Δ, 2³Δ, and 3³Δ states of AgH. This approach is also applied to other calculations where MRMP is influenced by intruder states; calculations are performed on the ³Π_u state of N₂, the ³Π state of CO, and the 2¹A′ state of formamide. A number of calculations are also performed to illustrate that this approach has little or no effect on MRMP when intruder states are not present in perturbative calculations; vertical excitation energies are computed for the low‐lying states of N₂, C₂, CO, formamide, and benzene; the adiabatic ¹A₁–³B₁ energy separation in CH₂, and the spectroscopic parameters of O₂ are also calculated. Vertical excitation energies are also performed on the Q and B bands states of free‐base, chlorin, and zinc–chlorin porphyrin, where somewhat larger couplings exists, and—as anticipated—a larger deviation is found between MRMP and ISA‐MRMP. © 2002 Wiley Periodicals, Inc. J Comput Chem 10: 957–965, 2002     

Molecular properties from coupled-cluster Brueckner orbitals

We investigate to which extent a single determinant made up from orbitals obtained by a Brueckner coupled-cluster doubles calculation is able to reproduce correlated one-electron properties. It is shown that dipole and quadrupole moments and radial expectation values compare quite well with BCCD finite-field results for a test selection of nine molecules enclosing HF, H₂O, NH₃, CO, N₂, NO⁺, HCN, CuH and CH₃OH and three rare-gas atoms He, Ne and Ar. Furthermore, we find that even second-order properties such as dipole and quadrupole polarizabilities are reproduced fairly well when determined as first derivatives of the corresponding Brueckner orbital expectation values.     

Molecular orbital theory of the hydrogen bond. 24. Ground-state water–uracil complexes

Ab initio SCF calculations with the STO -3G basis set have been performed to investigate the structural, energetic, and electronic properties of mixed water–uracil dimers formed at the six hydrogen-bonding sites in the uracil molecular plane. Hydrogen-bond formation at three of the carbonyl oxygen sites leads to cyclic structures in which a water molecule bridges N₁? H and O₂, N₃? H and O₂, and N₃? H and O₄. Open structures form at O₄, N₁? H, and N₃? H. The two most stable structures, with energies of 9.9 and 9.7 kcal/mole, respectively, are the open structure at N₁? H and the cyclic one at N₁? H and O₂. These two are easily interconverted, and may be regarded as corresponding to just one “wobble” dimer. At 1 kcal/mole higher in energy is another “wobble” dimer consisting of an open structure at N₃? H and a cyclic structure at N₃? H and O₄. The third cyclic structure at N₃? H and O₂ collapses to the “wobble” dimer at N₃? H and O₄. The two “wobble” dimers are significantly more stable than the open dimer formed at O₄, which has a stabilization energy of 5.4 kcal/mole. Uracil is a stronger proton donor to water through N₁? H than N₃? H, owing to a more favorable molecular dipole moment alignment when association occurs through H₁. Hydration of uracil by additional water molecules has also been investigated. Dimer stabilization energies and hydrogen-bond energies are nearly additive in most 2:1 water:uracil structures. There are three stable “wobble” trimers, which have stabilization energies that vary from 7 to 9 kcal/mole per water molecule. Hydrogen-bond strengths are slightly enhanced in 3:1 water:uracil structures, but the cooperative effect in hydrogen bonding is still relatively small. The single stable water–uracil tetramer is a “wobble” tetramer, with two water molecules which are relatively free to move between adjacent hydrogen-bonding sites, and a stabilization energy of approximately 8 kcal/mole per water molecule. Within the rigid dimer approximation, successive hydration of uracil is limited to the addition of one, two, or three water molecules.     

An ab initio study of O2 and CO2 transport by perfluorocarbons

Fluorocarbons have been successfully applied as oxygen carriers replacing blood. In order to understand the nature of the interaction between fluorocarbons and hydrocarbons on the one hand and O₂, N₂ and CO₂ on the other, STO-3G calculations have been performed on their complexes. The very slight energies of interaction that were obtained seem to substantiate the contention that O₂, N₂ and CO₂ are physically dissolved in fluorocarbons. This energy of interaction is, however, distinctly larger for fluorocarbons than for hydrocarbons. Electrostatic potentials have been computed around several fluorocarbons. They make it possible to predict the geometries of the complexes that are formed.     

Vacuum UV emission from reactions of metastable inert gas atoms: Chemiluminescence of ArO and ArCl

Vacuum UV chemiluminescence from bound upper states of ArO, KrO and ArCl is observed from the quenching of excited inert gas atoms by N₂O, O₃, Cl₂ and CCl₄. In these systems, the metastable ³P₂ states of Ar and Kr strongly resemble ground state alkali atoms in their chemical properties.     

Thermodynamic Approach to the Calculation of the Rate Constants of Monomolecular Reactions in the Strong-Collision Limit

A thermodynamic approach to the calculation of the dissociation (recombination) rate constants of polyatomic molecules in the strong-collision limit is suggested. The approach is based on the density of states obtained by the inverse Laplace transform of the integral expression for the statistical sum of the internal degrees of freedom of the molecule. Although the mathematical apparatus of this model is rather simple, it enables one to take into account the real energy distribution of molecular states. The potential of this method is demonstrated for O₃, H₂O, H₂O₂, CH₄, and C₂H₆. The results obtained are compared with data calculated using other methods. The temperature dependence of the collision efficiency correction β_c is analyzed for water and ethane.     

Spectrum of states in icosahedral structures with gN electronic configuration (n = 1– 7). 2. Ab initio calculation of the c20 (I h) molecule and its anions

Ab initio 4- 31G calculations of the C₂₀ (I_h) molecule and its onions in different spectroscopic states arising from the ground electronic configuration g^N are reported. The purpose of these calculations is an independent (quantum chemical) verification of the invariant expansions for the energy obtained in the previous work [15], in particular, of the conclusion derived from these expansions that states with different symmetries in the g^N (I, I_h) configuration are degenerate. Translated fromZhumal Struktumoi Khimii, Vol. 38, No. 4, pp. 605–615, July–August, 1997.     

The low temperature synthesis of metal oxides by novel hydrazine method

The hydroxide, oxalate and citrate precursors of the metal oxides such as γ-Fe₂O₃, (MnZn)Fe₂O₄, Cu(K)Fe₂O₄, BaTiO₃, La(Sr)MnO₃, La(Sr)AlO₃, La/Gd(Ca/Ba/Sr)CoO₃, and anatase TiO₂ on modifications with the hydrazine decompose at low temperatures give single phase oxides of superior properties, while the complexes without such modification require higher temperatures for achieving the phases. The hydrazine released at lower temperatures reacts with the oxygen in the atmosphere, N₂H₄+O₂→N₂+2H₂O; ΔH=−625 kJ mol⁻¹, and liberates enormous energy that is sufficient for the oxidative decomposition of the complexes now devoid of hydrazine. Such extra energy is not available in the case of the precursors without such modifications. The reaction products of hydrazine oxidation provide desired partial pressure of moisture needed for the stabilization of γ-Fe₂O₃. Also, the nitrogen that is formed in the reaction of hydrazine with oxygen gets trapped in the lattice of TiO₂ giving yellow color nitrogen doped TiO_2−xN_x photocatalyst. Thus, hydrazine method of preparation has many advantages in the preparation of metal oxides of superior properties.     

The two-photon excitation spectrum of triphenylene in n-heptane single crystals: Chem. Phys. Letters 57 (1978) 496

Chemiluminescence spectra and photon yields resulting from reactions of copper atoms with N₂O, O₂, NO, NF₃, SF₆, F₂, Cl₂, Br₂, and I₂ have been obtained between 200 and 1100 nm. The most interesting feature of these spectra is the strong and peculiar emission from copper atoms observed in the Cu + NF₃ reaction; population inversion has been obtained between some of the Cu states and it is suggested that this is due to energy transfer from N₂(A) formed in the reaction to copper atoms.     

Ab initio calculations on NO2 and NO 2 − : Optimization of diffuse Gaussian exponents

Ab initio calculations of NO₂ and NO ₂ ⁻ , using a Dunning [4s3p] basis augmented by 1 component diffuses andp functions were carried out. The SCF energies of NO₂ and NO_2/− (ground states) as a function of O _s , O _p , N _s , and N _p diffuse function exponents are given and discussed. The curves show some unexpected features which make the optimization of the diffuse function exponents problematic. The SCF vertical electron detachment energy for NO ₂ ⁻ as a function of the diffuse O _s , O _p , N _s , and N _p exponents is then discussed. Except for the case of O _p , the detachment energy is essentially independent of the O _s , N _s , and N _p exponents. Finally, results of SCF and MCSCF/CI calculations of the electron affinity of NO₂ are given and compared with experiment. Work performed under the auspices of the Division of Basic Energy Sciences of the U.S. Department of Energy. By acceptance of this article, the publisher and/or recipient acknowledges the U.S. Government's right to retain a nonexclusive, royalty-free license in and to any copyright covering this paper.     

Character of the electronic ground state and of charge-transfer excited states in ionic solids: An ab initio cluster model approach

The electronic structure of the ground electronic state and of some special charge-transfer excited states in ionic solids is examined from the ab initio cluster model approach. Different ab initio wave functions, including a frozen orbital approach, the Hartree–Fock self-consistent field, and multireference configuration interaction wave functions, are considered and analyzed using different theoretical techniques. We explicitly consider some alkaline–earth oxides such as CaO, a more difficult case such as A1₂O₃, a transition-metal oxide such as NiO, and a system with a more complicated structure such as KNiF₃. Analysis of ab initio wave functions in terms of valence bond components shows that all these compounds are largely ionic, thus supporting the simple picture arising from the ionic model. However, the nature of the excited states is more complex. Alkaline–earth oxides lowest excited states are essentially described as charge-transfer excitations dominated by a single resonant valence bond structure and the calculated energy difference is comparable to the experimental optical gap. In the case of A1₂O₃, the electronic spectra presents excitonic features and the local charge-transfer excitation excited states provide a reasonable representation of these phenomena. Finally, several different valence bond structures are present in the lowest electronic states of KNiF₃. © 1994 John Wiley & Sons, Inc.     

Self-consistent field calculations using two-body density functionals for correlation energy component: II. Small molecules

In part I of this series, self-consistent calculations using two-body density functionals for correlation energy were done and applied to atomic systems, giving very good results. We now apply the same scheme to small molecules. The examples studied include diatomic (H₂, Li₂, B₂, C₂, N₂, O₂, F₂, HLi, HBe, HB, HF, and HCl) as well as polyatomic (H₂O, NH₃, H₂O₂, and O₃) molecules at their ground states. The values reported for equilibrium geometries, atomization energies, vibrational frequencies, and dipole moments are compared with experimental and other theoretical calculations, with good agreement in most cases. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1899–1908, 1998     

Promoted Fixation of Molecular Nitrogen with Surface Oxygen Vacancies on Plasmon‐Enhanced TiO2 Photoelectrodes

A hundred years on, the energy‐intensive Haber–Bosch process continues to turn the N₂ in air into fertilizer, nourishing billions of people while causing pollution and greenhouse gas emissions. The urgency of mitigating climate change motivates society to progress toward a more sustainable method for fixing N₂ that is based on clean energy. Surface oxygen vacancies (surface O_vac) hold great potential for N₂ adsorption and activation, but introducing O_vac on the very surface without affecting bulk properties remains a great challenge. Fine tuning of the surface O_vac by atomic layer deposition is described, forming a thin amorphous TiO₂ layer on plasmon‐enhanced rutile TiO₂/Au nanorods. Surface O_vac in the outer amorphous TiO₂ thin layer promote the adsorption and activation of N₂, which facilitates N₂ reduction to ammonia by excited electrons from ultraviolet‐light‐driven TiO₂ and visible‐light‐driven Au surface plasmons. The findings offer a new approach to N₂ photofixation under ambient conditions (that is, room temperature and atmospheric pressure).     

Single-determinantal open- and closed-shell FSGO calculations for some diatomic molecules

Open-shell single-determinantal calculations are reported here for the molecular species H₂, Li₂⁺, N₂, O₂ (triplet), O₂^2?;, O₂^?, O₂²⁺, O₂⁺, and F₂; corresponding closed-shell calculations are reported for the species H₂, N₂, O₂ (singlet), O₂^2?, O₂²⁺, and F₂. The floating spherical Gaussian orbital (FSGO ) method was employed. The calculated trend in bond lengths of isonucleic diatomic molecules is in agreement with experiment. For heteronucleic diatomic molecules, however, the experimental trend in bond lengths is not obtained; in this connection, the effect of lone pairs on bond length is discussed. The dissociation energies of H₂ and Li₂⁺ are evaluated. The energy gap between the triplet and singlet states of the oxygen molecule is calculated to be 8.96 eV compared to the experimental value of 4.54 eV.     

The caged state of some small molecules in the C60 cage

The potential energy curves of some small molecules, H₂, N₂, O₂, F₂, HF, CO and NO, in the caged state within C₆₀ cage and in the free state have been calculated by the quantum-chemical method AM1. In this study, the focus is on the cage effect of C₆₀, and the concept of caged state is put forward. The results show that the bond lengths in the caged states are not much different from those in their corresponding free states, but the bond intensities in the caged states are much greater than those in their corresponding free states.     

Structural investigation of high‐transmittance aluminum oxynitride films deposited by ion beam sputtering

Aluminum oxynitride films were deposited by ion beam sputtering technique at room temperature. The optical properties and morphologies of the aluminum oxynitride films were studied and reported previously. It was found that the optical properties are closely related to the O contents in the films. In this study, the structures of the films were investigated by X‐ray diffractometer and XPS. Three oxidation states of N_1s in oxynitride films, N⁺, N²⁺ and N³⁺, were clearly deduced from N_1s spectra in the amorphous films fabricated under various oxygen partial pressures (P_O2). To our knowledge, three oxidation states of N_1s have not been simultaneously observed and reported in the aluminum oxynitride films previously. Corresponding bonding variations in Al_2p and O_1s spectra indicated more oxygen in oxynitride in the film as P_O2 increases. Three aluminum oxynitride networks, AlO₂N, AlO_2.5N and AlO₃N were deduced. Optical properties of aluminum oxynitride films resemble those of AlN and Al₂O₃ films when P_O2 is low and high during the deposition. The refractive indices and extinction coefficients of the aluminum oxynitride films can be adjusted by using proper P_O2 during the film depositions. Copyright © 2010 John Wiley & Sons, Ltd.     

The canonical exchange energy modulation parameters in molecular MTXα calculations. Some first row homonuclear diatomic molecules

The canonical MTXα scheme which uses the parameters α_I = $\text{2}\text{3}$ for all atoms, and α_II = 1 for all molecules is developed and applied to the calculation of the potential energy curves and ionization potentials for the ground electronic states of B₂, C₂, N₂, O₂ and F₂.     

Quantum-chemical DFT calculations of the molecular structure of N<Subscript>2</Subscript>O<Subscript>5</Subscript> in the gas and solid phases

By functional density quantum-chemical method (DFT/B3LYP using the 6-311++G(3df)) it has been shown that the molecular structures of N₂O₅ with C_s and C₂ symmetries are energetically equivalent. It follows from calculations of the vibrational frequencies that both structures are characterized by potential energy minima and correspond to stationary states of the N₂O₅ molecule. It is proposed, on the basis of a comparison of the calculated and experimental vibrational spectra of N₂O₅, that dinitrogen pentaoxide exists in the gas phase as an equimolecular mixture of N₂O₅ molecules with Cs and C₂ symmetry, while in the solid phase it is characterized by the C₂ molecular structure. __________ Translated from Teoreticheskaya I éksperimental’naya Khimiya, Vol. 43, No. 1, pp. 58–63, January–February, 2007.