Segmented waveguide arrays: deriving discrete diffraction relations in a square lattice photonic crystal.

Segmented strip-loaded waveguide arrays are investigated within a rigorous square lattice photonic crystal model. We derive a full multiband discrete diffraction approach for near-axial injection in the direction of a lattice vector. We obtain an effective waveguide array picture, with quasi-linear dependence on the segmentation ratio in a simplified single-band scheme. Our results are validated by beam deviation experiments. Such a diffraction framework allows for efficient shaping of the phase map in waveguide arrays and enriches the engineering toolkit of photonic crystals with the in-plane free propagation structures of discrete photonics.

Modeling localized photoinduced electrons in rutile-TiO2 using periodic DFT+U methodology.

We propose a theoretical model for photocatalytic processes on titanium dioxide, described by its most stable phase and surface, rutile-TiO(2)(110). The excitation induced by light promotes electrons from the valence band to the conduction band. In this context, one important requirement is having a correct value of the magnitude of the electronic gap. The use of GGA+U or LDA+U functional with an appropriate U value allows this. The U correction has little consequence on the adsorption strength itself on the TiO(2)(110) surface. For the ground state, it only yields a slight increase of the interaction strength of some test molecules; the surface basicity is somewhat enhanced. This is interpreted by the shift of TiO(2) vacant levels. Photoexcitation is taken into account by imposing two unpaired electrons per cell of the same spin. The size of the cell therefore determines the number of excitations per surface area; the larger the cell, the smaller the electron-hole surface concentration and the smaller the energy for electronic excitation. For the excited state, careful attention must be focused on the localization of the excited electron and of the hole which are crucial for the determination of the lowest electronic states and for the surface reactivity. We found that the excited electron is localized on a pentacoordinated surface titanium atom while the hole is shared by two surface oxygen atoms not too far from it. The electronic levels associated to the reduced titanium atoms are low in energy; the projected density of states is superposed onto the valence band.

Discrete photonics in waveguide arrays.

In homogeneous arrays of coupled waveguides, Floquet-Bloch waves are known to travel freely across the waveguides. We introduce a systematic discussion of the built-in patterning of the coupling constant between neighboring waveguides. Key patterns provide functions such as redirecting, guiding, and focusing these waves, up to nonlinear all-optical routing. This opens the way to light control in a functionalized discrete space, i.e., discrete photonics.

The molecular structure and vibrational spectra of 3-acetyl-4-[N-(2'-aminopyridinyl)-3-amino]-3-buten-2-one by Hartree-Fock and density functional theory calculations.

The molecular structure and vibrational spectra of 3-acetyl-4-[N-(2'-aminopyridinyl)-3-amino]-3-buten-2-one (C(11)H(13)N(3)O(2)) in the ground state have been investigated by Hartree-Fock and density functional method (B3LYP and BLYP) with 6-31G(d) basis set. The optimized geometric bond lengths and bond angles obtained by using HF and DFT show the best agreement with the experimental data. Comparison of the observed fundamental vibrational frequencies of title compound and calculated results by HF and DFT methods indicate that B3LYP is superior to the scaled HF approach for molecular problems.

Structural, vibrational and ab initio studies of L-histidine oxalate.

Single crystals of L-histidine oxalate were obtained by slow evaporation of an aqueous solution at room temperature. The grown crystals have been subjected to X-ray diffraction (XRD), Infrared, and Raman spectroscopy. The title compound crystallises in the non-centrosymmetric space group P2(1)2(1)2(1,) the crystal cohesion is achieved by relatively strong hydrogen bonds, so that the NH3 groups show significant distortion with respect to the tetrahedral symmetry. Raman and infrared spectra of the title compound were recorded in the frequency range 300-3200 and 400-4000 cm-1, respectively. To obtain a reliable assignment of the observed spectral lines, we have calculated the geometry and the frequencies of the vibrational modes of histidine cation and the oxalate anion using the semi empirical PM3 method.

Strong Coupling between Self-Assembled Molecules and Surface Plasmon Polaritons.

We experimentally demonstrate strong coupling between self-assembled PTCDI-C7 organic molecules and the electromagnetic mode generated by surface plasmon polaritons (SPPs). The system consists of a dense self-assembly of ordered molecules evaporated directly on a thin gold film, which stack perpendicularly to the metal surface to form H-aggregates, without a host matrix. Experimental wavevector-resolved reflectance spectra show the formation of hybrid states that display a clear anticrossing, attesting the strong coupling regime with a Rabi splitting energy of ΩR ≃ 102 meV at room temperature. We demonstrate that the strength of the observed strong coupling regime derives from the high degree of organization of the dense layers of self-assembled molecules at the nanoscale that results in the concentration of the oscillator strength in a charge-transfer Frenkel exciton, with a dipole moment parallel to the direction of the maximum electric field. We compare our results to numerical simulations of a transfer matrix model and reach good qualitative agreement with the experimental findings. In our nanophotonic system, the use of self-assembled molecules opens interesting prospects in the context of strong coupling regimes with molecular systems.

Periodic DFT study of the structural and electronic properties of bulk CoAl2O4 spinel.

In this study, structural and electronic properties of CoAl2O4 spinel are investigated for the first time by means of quantum chemical computational tools. Coupling supercell periodic calculations under the density functional theory formalism with a nonempirical quasi-harmonic Debye model, we examine the influence of temperature on the relative stability of several cation distributions of Co2+ and Al3+ over tetrahedral and octahedral interstices of the oxygen sublattice. Our simulations are able to reproduce the experimentally observed trend: (i) the normal spinel is calculated to be the stable structure at static and low-temperature conditions, and (ii) as the temperature increases, the preference of structures with Al3+ at tetrahedral sites (and Co2+ at octahedral sites) is found to progress following an asymptotic conduct. The effects of the cation distributions on geometrical variations of electronic and magnetic properties of CoAl2O4 can be interpreted as dominated by the local behavior of Co2+ at octahedral sites.

Crystal structure, vibrational studies, optical properties and DFT calculation of bis 2-aminobenzothiazolium tetrachloridocuprate.

The zero dimensional organic-inorganic hybrid compound (C7H7N2S)2CuCl4 was synthesized and characterized by X-ray diffraction, infrared absorption, Raman spectroscopy scattering and optical transmission measurements. The title compound crystallizes in the monoclinic system with P21/c space group. The unit cell parameters are a=7.060 (5) Å, b=9.748 (5) Å, c=14.037 (5) Å, ß=98.520 (5)° and Z=2. The copper (II) ion has square planar coordination environment and the structure is built up from isolated [CuCl4](2)(-) anion surrounded by organic cations connected together via N-H⋯Cl hydrogen bonding. Room temperature IR and Raman spectra of the title compound were recorded and analyzed. The theoretical geometrical parameters in the ground state have been investigated by density functional theory (DFT) with the B3LYP/LanL2DZ level of theory. The organic-inorganic hybrid crystal thin film can be easily prepared by spin-coating method from the ethanol solution of the (C7H7N2S)2CuCl4 compound and it showed characteristic absorptions of Cu-Cl based layered perovskite centered at 288 and 400 nm.

Vibrational spectra and non linear optical proprieties of L-histidine oxalate: DFT studies.

This paper presents the results of our calculations on the geometric parameters, vibrational spectra and hyperpolarizability of a nonlinear optical material L-histidine oxalate. Due to the lack of sufficiently precise information on geometric structure in literature, theoretical calculations were preceded by re-determination of the crystal X-ray structure. Single crystal of L-histidine oxalate has been growing by slow evaporation of an aqueous solution at room temperature. The compound crystallizes in the non-Centro symmetric space group P2(1)2(1)2(1) of orthorhombic system. The FT-IR and Raman spectra of L-histidine oxalate were recorded and analyzed. The vibrational wave numbers were examined theoretical with the aid of Gaussian98 package of programs using the DFT//B3LYP/6-31G(d) level of theory. The data obtained from vibrational wave number calculations are used to assign vibrational bands obtained in IR and Raman spectroscopy of the studied compound. The geometrical parameters of the title compound are in agreement with the values of similar structures. To investigate microscopic second order non-linear optical NLO behaviour of the examined complex, the electric dipole µ(tot), the polarizability α(tot) and the hyperpolarizability ß(tot) were computed using DFT//B3LYP/6-31G(d) method. According to our calculation, the title compound exhibits non-zero ß(tot) value revealing microscopic second order NLO behaviour.

Molecular structure, vibrational spectra and nonlinear optical properties of orthoarsenic acid-tris-(hydroxymethyl)-aminomethane DFT study.

In this work, we report a theoretical study on molecular structure, vibrational spectra and nonlinear optical properties of orthoarsenic acid-tris-(hydroxymethyl)-aminomethane (OATA). The theoretical geometrical parameters in the ground state have been investigated by density functional method (B3LYP and BLYP) with 6-311G(d,p) basis set. The influence of intermolecular interactions effects on molecular properties has been considered by calculation performed on (OATA) dimer. The optimized geometric bond lengths and bond angles are in well agreement with the experimental data. As compared to theoretical frequencies of the monomer, the calculated values obtained for (OATA) dimer are in much better agreement with the experiment. All experimental vibrational bands have been discussed and assigned to normal modes on the basis of our theoretical calculations. B3LYP method has shown better fit to experimental ones than BLYP in calculation vibrational frequencies. To investigate nonlinear optical behaviour, the electric dipole moment mu, the polarizability alpha and the hyperpolarizability beta were computed using DFT//B3LYP/6-311G(d,p) method.

Crystal studies, vibrational spectra and non-linear optical properties of L-histidine chloride monohydrate.

This paper presents the results of our calculations on the geometric parameters, vibrational spectra and hyperpolarizability of a non-linear optical material L-histidine chloride monohydrate. Due to the lack of sufficiently precise information on geometric parameters available in literature, theoretical calculations were preceded by re-determination of the crystal X-ray structure. Single crystal of L-histidine chloride monohydrate has been growing by slow evaporation of an aqueous solution at room temperature. The compound crystallizes in the non-Centro-symmetric space group P2(1)2(1)2(1) of orthorhombic system. IR spectrum has been recorded in the range [400-4000 cm(-1)]. All the experimental vibrational bands have been discussed and assigned to normal mode or to combinations on the basis of our calculations. The optimized geometric bond lengths and bond angles obtained by using DFT//B3LYP/6-31G (d) method show a good agreement with the experimental data. The calculated vibrational spectra are in well agreement with the experimental one. To investigate microscopic second-order non-linear optical NLO behavior of the examined complex, the electric dipole mu, the polarizability alpha and the hyperpolarizability beta were computed using DFT//B3LYP/6-31G (d) method. The time-dependent density functional theory (TD-DFT) was employed to descript the molecular electron structure of the title compound using the B3LYP/6-31G (d) method. According to our calculations, L-histidine chloride monohydrate exhibits non-zero beta value revealing microscopic second-order NLO behavior.

Solvent effects on conformation of a sex pheromone ofCydia (Laspeyresia pomonella L.; Lepidoptera: Tortricidae: Olethreutinae), codlemone (8,10-dodecadienol).

The conformations of codlemone (8,10-dodecadienol) and of a model analog have been studied by CNDO calculations. Stable conformations are found for the folded forms when the polarity of the solvent is taken into account.

Revisited physicochemical and transport properties of respiratory mucus in genotyped cystic fibrosis patients.

We investigated the physicochemical and transport properties of sputum samples collected in physiotherapy from a well-documented group of 27 cystic fibrosis (CF) patients with identified CF genotypes. Sputum samples were characterized ex vivo for their water content, surface properties (surface tension and contact angle), rheologic properties (viscosity and elastic modulus), and transport properties (mucociliary and cough transport). These data were analyzed in relation to the clinical status of the patients (FEV1, FVC, Shwachman score, Brasfield score, nutritional status), their genotype, and the degree of infection of their sputa (leukocyte and Pseudomonas aeruginosa counts). We observed negative and significant correlations between mucociliary transport and elastic modulus of the patients' sputum (r = -0.63, p < 0.01), and between the cough transport and contact angle of the sputum (r = -0.81, p < 0.0001), respectively. The P. aeruginosa count was also significantly correlated with the sputum water content (r = -0.53, p < 0.02) as well as with the cough transport of the sputum (r = -0.62, p < 0.01). In CF patients with a sputum leukocyte count > 2,000/mm3, the sputum water content (p < 0.02), FEV1 (p < 0.05) and FVC (p < 0.02) were significantly lower than those of CF patients with a leukocyte count < or = 2,000/mm3. CF patients with a homozygous delta F 508 genotype had significantly greater values of sputum water content (p < 0.05), and cough-transport capacity (p < 0.05) than did heterozygous patients. No correlation was observed between the sputum properties and any of the clinical data. These results suggest that the control of infection should be emphasized in CF, since it can directly or indirectly modulate the degree of hydration, and therefore the physicochemical and transport properties, of airway secretions.