Interactive quantum chemistry: a divide-and-conquer ASED-MO method

We present interactive quantum chemistry simulation at the atom superposition and electron delocalization molecular orbital (ASED-MO) level of theory. Our method is based on the divide-and-conquer (D&C) approach, which we show is accurate and efficient for this non-self-consistent semiempirical theory. The method has a linear complexity in the number of atoms, scales well with the number of cores, and has a small prefactor. The time cost is completely controllable, as all steps are performed with direct algorithms, i.e., no iterative schemes are used. We discuss the errors induced by the D&C approach, first empirically on a few examples, and then via a theoretical study of two toy models that can be analytically solved for any number of atoms. Thanks to the precision and speed of the D&C approach, we are able to demonstrate interactive quantum chemistry simulations for systems up to a few hundred atoms on a current multicore desktop computer. When drawing and editing molecular systems, interactive simulations provide immediate, intuitive feedback on chemical structures. As the number of cores on personal computers increases, and larger and larger systems can be dealt with, we believe such interactive simulations-even at lower levels of theory-should thus prove most useful to effectively understand, design and prototype molecules, devices and materials.     

When a Red–NIR-Emissive Cs2[Mo6Br14] Interacts with an Active Diureasil–PEO Matrix: Design of Tunable and White-Light-Emitting Hybrid Material

Hybrid materials that combine diureasil matrices and octahedral molybdenum clusters have been synthesized to design lead-, cadmium- and rare-earth-free emitters for lighting or optoelectronic applications. This association leads to homogeneous and stable hybrids, for which the emission color can be tailored in the entire visible range, including white light; this is thanks to effective energy transfers from the host to the nanocluster.     

Electric properties of the water molecule in 1A1, 1B1, and 3B1 electronic states: Refined CASSCF and CASPT2 calculations

Summary The dipole moments and dipole polarizabilities of the ¹A₁, ¹B₁, and ³B₁ electronic states of the water molecule have been calculated by using the CASSCF approach followed by the evaluation of the dynamic electron correlation contribution by the second-order perturbation scheme CASPT2. All calculations have been carried out in a specifically extended ANO basis set which accounts for the Rydberg character of the two excited states. In order to estimate the correctness and accuracy of the present data a scan over a variety of different active spaces for the CASSCF wave function has been made. The present results are superior to earlier CASSCF calculations, although their qualitative features remain essentially the same. The dipole moments in ¹B₁ and ³B₁ states are predicted to be about 0.49 a.u. and 0.33 a.u., respectively, and have the opposite orientation with respect to the ground state dipole moment. The dipole polarizability tensors of the excited states are characterized by high anisotropy and are dominated by the in-plane component perpendicular to the symmetry axis. All their components are found to be about an order of magnitude larger than those of the ground state polarizability tensor. The excitation energy dependence on the choice of the active orbital space in the CASSCF reference function is also considered and the analysis of the present data concludes in the concept of what is called the mutually compatible active spaces for the two states involved in excitation. All CASPT2 results are in good agreement with the results of recent calculations carried out in the framework of the open-shell coupled cluster formalism. This agreement confirms the high efficiency of the CASSCF/CASPT2 approach to the treatment of the electron correlation effects.     

The dielectric function of LnSF rare-earth fluorosulfides (Ln=La, Ce): experiment and theory

The absorption properties of LaSF and CeSF in the UV-Visible range have been investigated on the basis of first principles density functional theory (DFT) calculations and from electron energy-loss spectroscopy (EELS) measurements. The extinction coefficient k, as well as the refractive index n, determined experimentally from the loss function Im(−1/ε), were compared with the corresponding factors extracted from the calculated dielectric tensor ε₂. The k and n values for the two compounds were expected to be very close to each other, owing to the chemical similarity of La and Ce. However, it was found that the nature of the electronic transitions in LaSF and CeSF strongly influences the k and n values with the result that the refractive index n and the extinction coefficient k are substantially larger for LaSF than for CeSF.     

The Quest for Single-Source Precursors for BaTiO3 and SrTiO3

The reactions between titanium alkoxides Ti(OR)₄ (R = Et,i Pr) and strontium -diketonates Sr(-dik)₂ (-dik = thd, acac) were investigated. The various Sr-Ti species, Sr₂Ti₂(-dik)₄ (OR)₈, have a 1:1 Sr:Ti stoichiometry and were characterized by elemental analysis, FT-IR and by single-crystal X-ray diffraction for Sr₂Ti₂(₃-OiPr)₂ (-OiPr)₄ (OiPr)₂(thd)₄ (1). The hydrolysis-polycondensation reactions of the various species were investigated and the resulting powders analyzed by light scattering and XRD. While acetone was found to have little influence on the hydrolysis reactions of the Sr-Ti species, polycondensation of Ti(OiPr)₄ in neat acetone offers a trinuclear enolate Ti(₃-O)₂(OCMe=CH₂)₃ (OiPr)₅(iPrOH) (4). Comparisons between the Ba-Ti and Sr-Ti systems are given.     

Synthesis and structural characterization of some titanium butoxides modified with chloroacetic acids

Reactions of Ti(OBu^s)₄ and Ti(OBuⁿ)₄ with chloroacetic acids (mono-, di-, and tri-) were carried out in toluene in 1:1 and 1:2 molar ratios at room temperature to generate new precursors of titania. These modified alkoxides/oxo-alkoxides were characterized by spectroscopic methods. A solution of Ti(OBuⁿ)₂(OOCCCl₃)₂ in toluene left for crystallization at ?30 °C yielded single crystals of the product Ti₆(μ₂-O)₂(μ₃-O)₂(μ₂-OC₄H₉)₂(OC₄H₉)₆(OOCCCl₃)₈. Single-crystal X-ray diffraction revealed the molecular structure to be composed of a hexanuclear unit in which two Ti₂O₁₀ units (made by two edge-sharing octahedra) are linked with two corner-sharing octahedra.     

Spray-dried oil powder with ultrahigh oil content

We report a new facile route to the production of solid oil powders with an oil weight content of as high as 90% or beyond. The proposed method starts from a standard protein-stabilized oil-in-water emulsion in which a protein monolayer absorbed at the oil-water interface is successively cross linked by a thermal treatment. The emulsion is then spray dried as for ordinary emulsions, however without the addition of hydrocolloids typically needed when spray drying liquid oil dispersions. This leads to a final solid oil powder in which the total mass is constituted of oil, proteins, and eventual buffer salts and in which the elasticity of the cross-linked protein monolayer is alone sufficient to stabilize the powder and to limit any oil leakage. To best illustrate the potential in food applications and to preserve the food-grade nature of the constituents, we have used thermal denaturation at 80 °C for 15 min to cross link a β-lactoglobulin-stabilized olive oil-in-water emulsion and to produce the corresponding solid oil powder. Because of the simplicity and flexibility of the proposed pathway, the present method can be used inexpensively to convert any type of hydrophobic liquid into the corresponding solid powder and is then particularly suitable for cosmetic, pharmaceutical, medical, biotechnological, and food applications.