Relativistic correlating basis sets for 57La and 89Ac

Wurtzite-perovskite heterostructures composed of a high dielectric constant oxide and a wide bandgap semiconductor envision promising applications in field-effect transistors. In the present paper, the structural and electronic properties of LaAlO3/ZnO heterojunctions are investigated by first-principles calculations. We study the initial adsorption of La, Al, and oxygen atoms on ZnO (0001) and (0001¯) surfaces and find that La atoms may occupy interstitial sites during the growth of stoichiometric ZnO (0001). The band gap of the stoichiometric ZnO (0001) surface is smaller than that of the stoichiometric ZnO (0001¯) surface. The surface formation energy indicates that La or Al atoms may substitute Zn atoms at the nonstoichiometric ZnO (0001) surface. The atomic charges, electronic density of states, and band offsets are analyzed for the optimized LaAlO3/ZnO heterojunctions. There is a band gap for the LaAlO3/ZnO (0001¯) heterostructures, and the largest variation in charge occurs at the surface or interface. Our results suggest that the Al-terminated LaAlO3/ZnO (0001¯) interfaces are suitable for the design of metal oxide semiconductor devices because the valence and conduction band offsets are both larger than 1 eV and the interface does not produce any in-gap states.

This work presents a detailed study on the chemical composition and bond structures of CeO2/La2O3 stacked gate dielectrics based on x-ray photoelectron spectroscopy (XPS) measurements at different depths. The chemical bonding structures in the interfacial layers were revealed by Gaussian decompositions of Ce 3d, La 3d, Si 2s, and O 1s photoemission spectra at different depths. We found that La atoms can diffuse into the CeO2 layer and a cerium-lanthanum complex oxide was formed in between the CeO2 and La2O3 films. Ce3+ and Ce4+ states always coexist in the as-deposited CeO2 film. Quantitative analyses were also conducted. The amount of CeO2 phase decreases by about 8% as approaching the CeO2/La2O3 interface. In addition, as compared with the single layer La2O3 sample, the CeO2/La2O3 stack exhibits a larger extent of silicon oxidation at the La2O3/Si interface. For the CeO2/La2O3 gate stack, the out-diffused lanthanum atoms can promote the reduction of CeO2 which produce more atomic oxygen. This result confirms the significant improvement of electrical properties of CeO2/La2O3 gated devices as the excess oxygen would help to reduce the oxygen vacancies in the film and would suppress the formation of interfacial La-silicide also.

Bi 0.9− x La 0.1 Tb x FeO 3 with x = 0.0 and 0.075 were synthesized by the solid-state reaction. Although it was difficult to obtain pure BiFeO 3 with single phase, the La-substituted Bi 0.9 La 0.1 FeO 3 can be obtained easily without any impurity phase. The Tb-substituted Bi 0.825 La 0.1 Tb 0.075 FeO 3 showed a well-saturated ferromagnetism. The average and local structures of the Bi 0.9 La 0.1 FeO 3 and Bi 0.825 La 0.1 Tb 0.075 FeO 3 crystals were analyzed by Rietveld refinement and pair-distribution function (PDF) method, respectively. The La and Tb atoms were completely substituted for the Bi, and lattice strain owing to different ionic radii was relaxed only by the bond distribution between the A-site atoms and the oxygen atoms.

A computational study of diatomic NiAl is reported. Molecular properties evaluated include the equilibrium bond length (re), equilibrium stretching frequency (ωe), doublet-quartet energy splitting, and nickel-aluminum bond strength. Several interesting conclusions have resulted from this research. First, convergence in calculated properties is smoother with recently reported correlation consistent basis sets than earlier basis sets for Ni and Al. Second, with the exception of bond strength, basis set limit properties extrapolated using correlation basis sets are in agreement with reported data. Third, this research suggests that caution may be needed with regard to the use of DFT for developing interatomic potentials for larger scale simulations. For example, B97-1 showed better agreement with reported re for 2NiAl than B3LYP. However, the situation was reversed for the calculation of ωe. With respect to bond strength, the situation is unclear due to the scatter among experiment and calculations. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Atom positions and anisotropic Debye-Waller factors of the rhombohedral phase of LaCrO(3) have been refined simultaneously with the low-order structure factors, using a structure-analysis method of convergent-beam electron diffraction (CBED) proposed by Tsuda & Tanaka [Acta Cryst. (1999), A55, 939-954]. The method is based on the least-squares fitting between full dynamical calculations and energy-filtered intensities of two-dimensional higher-order Laue-zone (HOLZ) and zeroth-order Laue-zone (ZOLZ) CBED patterns. The positions of the oxygen atoms have been determined with a high precision. Clear anisotropy of the thermal vibrations of the oxygen atoms has been successfully determined by the CBED method for the first time. The charge transfer from the La and Cr atoms to the O atoms has been found from the deformation charge-density map.

Assessment of the proposed pseudo-potential theoretical model for the static and dynamic Raman scattering intensities: Multivariate statistical approach to quantum-chemistry protocols.

Theoretical study on the interaction of oxygen atom with C90 (D5h)

Theoretical study of coinage metal dihalides is challenging due to their complex electron correlation and relativistic effects, particularly the spin-orbit coupling (SOC) effect. Furthermore, vibrational frequencies and characters of their low-lying states are affected by the Renner-Teller effect (RTE) and pseudo-Jahn-Teller effect (PJTE). The theoretical results depend on the basis set and how the electron correlation is treated and previous results even differ qualitatively in the ground state for some silver dihalides. The equation-of-motion coupled-cluster method at the singles and doubles level (EOM-CCSD) for ionization potentials is employed in this work to calculate electron affinities and vertical excitation energies of MX2 (M = Ag, Au; X = Cl, Br and I) as well as structures, harmonic frequencies and adiabatic excitation energies for the lowest two states of these molecules. Effects of the higher level correlation, basis set as well as SOC on these results, particularly on the πu bending mode frequencies of the 2Πg state, are investigated. A new assignment for photodetachment spectroscopy of AuCl2- is proposed where contribution of the 2Δg state is considered. The ground state of AgCl2 is calculated to be the 2B2 state of the C2v structure in scalar-relativistic (SR) calculations, while the SOC quenches the RTE and PJTE and the ground state becomes the 2Π3/2g state of the D∞h structure. As for the other molecules, the ground state is calculated to be the 2Πg state in SR cases, and the 2Π3/2g state with SOC. Our results indicate that a higher level electron correlation, large basis set and SOC are important to achieve reliable results for these molecules.

A theoretical study of diazirine (H2CN2), diazirinyl radical (HCN2) and their related cations <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si11.gif" overflow="scroll"><mml:mrow><mml:mo stretchy="false">(</mml:mo><mml:msub><mml:mrow><mml:mi mathvariant="normal">H</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:msubsup><mml:mrow><mml:mi mathvariant="normal">CN</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msubsup><mml:mo>,</mml:mo><mml:msubsup><mml:mrow><mml:mi mathvariant="normal">HCN</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msubsup><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:math>: molecular structure, energetics and ionization potential

Golden-rule treatment of the O 2+O −2 electron-transfer reaction

This is a preliminary study toward implementation of analytic density functional response approach for molecules to obtain linear and nonlinear electric properties. The Kohn–Sham framework has been used with Gaussian basis sets. We propose a fully variational approach to obtain the response of electronic density in terms of the atomic orbital basis (contracted Gaussians). As a first step, this derivative of the Kohn–Sham operator is obtained by a finite field method using five different values of electric field. Using this, we obtain the energy derivatives up to third order using fully analytic expressions. We calculate the dipole moment, polarizability, and hyperpolarizability of the hydrogen fluoride (HF) molecule as a test case using different exchange–correlation functionals and basis sets within the present methodology. We also explore the feasibility of this response approach by studying the properties of the HF molecule for different H–F distances.

The equilibrium structures, vibrational properties, and interaction energies for four bimolecular complexes of HCN and HNC (HCN···HCN, HNC···HNC, HCN···HNC, and HNC···HCN) were studied with ab initio methods. Different electron correlation levels and basis sets up to CCSD(T)/6-311++G(2d,2p) were used in the geometry optimizations and interaction energy calculations, and the vibrational frequencies were calculated at the MP2 and MP3 levels of theory. To study the nature of the intermolecular interactions, an energy decomposition analysis was carried out. For the HNC···HCN complex, which possesses a hydrogen bridge between two carbons, the counterpoise-corrected interaction energy and its decomposition has been calculated as a function of the intermolecular distance. The effect of subunit deformation on the interaction energy has also been considered. The results indicate that the HNC dimer has considerably stronger intermolecular interaction than the HCN dimer, and the HNC···HCN complex is bonded as strongly as the HCN dimer. The comparison of the various properties of the complexes and the energy decomposition analysis in particular indicate that carbon can act as both a hydrogen acceptor and donor, and the resulting hydrogen bonds in these complexes are relatively strong.

We present the results obtained from spectroscopic investigations and quantum chemical calculations of the interaction of anisole (methoxybenzene) with small water clusters. The experiments have been carried out using resonant two-photon ionization (R2PI) and IR-UV double-resonance vibrational spectroscopy (IR/R2PI) in the region of the OH stretches. Apart from the vibrational spectra of the water moiety in the clusters, their intermolecular vibrations in the electronically excited S1 state are identified by IR/R2PI hole burning spectroscopy and assigned according to the vibrations calculated for the S1 state and compared with the vibrations calculated for the S0 state. The calculations for the S0 state were carried out at the second order Møller-Plesset level of theory using both the 6-31+G* and aug-cc-pVDZ basis sets and for the S1 state at the configuration interaction singles (CIS) level with the 6-31+G* basis set. In the electronic ground state (S0), the interaction of a water monomer to anisole is mediated through its oxygen atom, and that of a water dimer both through the oxygen atom (σ type of interaction) and the arene ring (π type of interaction). Thus in contrast to the interaction of fluorinated benzenes with water clusters, wherein a conformational transition from an in-plane σ to a on-top π bonding emerges starting with a water trimer, this conformational transition appears in case of anisole already with a water dimer. In the excited state (S1) of the investigated systems, there is a pronounced weakening of the interaction of the water cluster with the aromatic chromophore, which is also responsible for the blue shift of the electronic transitions. Consequently, the structures of the complexes of anisole with a water monomer or dimer are very different in both states. The weakening results from a diminished electron density of the oxygen atom and of the π system of anisole in the excited state. The calculated binding energies of the ground-state conformers indicate that these small water clusters are bound more strongly to anisole than to other π systems like benzene, toluene, fluorobenzene, and p-difluorobenzene. The many-body decomposition of the binding energy (S0) reveals that a progressive increase in the size of the water clusters results in a weakening of the σ O⋯H interaction and a concurrent strengthening of the π-H interaction. The complex containing a cyclic water trimer exhibits in the excited state also a π-type H-bonding interaction, but its stability emerges from a delocalization of the electron density from the water trimer to the anisole oxygen. Excepting the water dimer complexes, there is a good agreement between the calculated OH vibrational frequencies and the experimental IR spectra recorded for the ground state. The surprisingly good agreement of the calculated and the experimentally observed intermolecular modes in the excited state of these complexes provides convincing evidence that the experimental spectra emerge from structures similar to those predicted at the CIS/6-31+G* level.

We investigate by explicit parameter optimization to what extent basis sets of polarized double-ζ quality can introduce compensating errors in five different density functional methods. It is shown that minor changes in the contraction coefficients of the valence functions in the basis sets can have a significant impact and allow different density functional methods to achieve very similar performances. This holds for nuclear magnetic shielding constants and for isomerization energies, barrier heights, and noncovalent interactions. It is furthermore shown that errors due to neglect of vibrational and solvent effects can be absorbed in the combined method and basis set errors. These findings hold for data sets consisting of 50-150 data points. This raises the question of whether the common practice of identifying combinations of density functional methods and basis sets that have a good performance against a selected set of reference data should be considered as data fitting in the combined parameter space spanned by the method and basis set.

A mixed molecular dynamics/quantum mechanics model has been applied to the ammonium/water clustering system. The use of the high level MP2 calculation method and correlated basis sets, such as aug-cc-pVDZ and aug-cc-pVTZ, lends confidence in the accuracy of the extrapolated energies. These calculations provide electronic and free energies for the formation of clusters of ammonium and 1-10 water molecules at two different temperatures. Structures and thermodynamic values are in good agreement with previous experimental and theoretical results. The estimated concentration of these clusters in the troposphere was calculated using atmospheric amounts of ammonium and water. Results show the favorability of forming these clusters and implications for ion-induced nucleation in the atmosphere.