First-Principles Calculation of the Optical Rotatory Power of Periodic Systems: Modern Theory with Modern Functionals

An analysis of orbital magnetization in band insulators is provided. It is shown that a previously proposed electronic orbital angular-momentum operator generalizes the ``modern theory of orbital magnetization'' to include non-local Hamiltonians. Expressions for magnetic transition dipole moments needed for the calculation of optical rotation (OR) and other properties are developed. A variety of issues that arise in this context are critically analyzed. These issues include periodicity of the operators, previously proposed band dispersion terms as well as, if and where needed, evaluation of reciprocal space derivatives of orbital coefficients. Our treatment is used to determine the optical rotatory power of band insulators employing a formulation that accounts for electric dipole - electric quadrupole (DQ), as well as electric dipole-magnetic dipole, contributions. An implementation in the public \textsc{Crystal} program is validated against a model finite system and applied to the $\alpha$-quartz mineral through linear-response time-dependent density functional theory with a hybrid functional. The latter calculations confirmed the importance of DQ terms. Agreement against experiment was only possible with i) use of a high quality basis set, ii) inclusion of a fraction of non-local Fock exchange, and iii) account of orbital-relaxation terms in the calculation of response functions

Effect of adding sugar beet fibre and wheat bran to a starch diet on the absorption kinetics of glucose, amino-nitrogen and volatile fatty acids in the pig

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Les déplacements pendulaires font-ils partie du choix d'un lieu d'habitation?

La croissance du trafic pendulaire représente une tendance de don depuis plusieurs décennies. Ce chapitre discute les effets que pourrait avoir une plus grande mixité fonctionnelle (habitat et travail) des territoires. En analysant la manière dont les ménages choisissent leur lieu de domicile, il montre l'importance de la mixité fonctionnelle comme instrument de gestion de la mobilité mais en souligne aussi les limites. Le choix résidentiel est en effet complexe et résulte d'arbitrage entre de nombreux éléments

Intramolecular dependence of the frequency dependent polarizabilities of Li2(a 3Σu+) and Na2(a 3Σu+) and van der Waals dispersion coefficients for atom-diatom and diatom-diatom alkali dimers

cited By 16International audienceAn ab initio time dependent gauge invariant method (TDGI) has been used to compute the frequency dependent dipole and quadrupole polarizabilities of Li, Na, Li2(a 3∑u+) and Na2(a 3∑u+) and their dependence on the internuclear distance of the diatomic species. The dependence of the isotropic and anisotropic components of the static dipole polarizabilities on the diatomic distance was fitted to an analytical form which has an asymptotic form in agreement with the theoretical expression derived by Heijmen, T. G. A., Moszynski, R., Wormer, P. E. S., and van der Avoird, A., Molec. Phys., 89, 81. Long range two-body C6 coefficients have been evaluated for all combinations of atom-atom, atom-homonuclear diatom and homonuclear diatom-homonuclear diatom systems in which the diatomics are in the a 3∑u+ state. Furthermore, the C8 coefficients for the atom-atom and atom-diatom interactions and the three-body C9 coefficients for the four atom-diatom systems have been obtained. For the atom-diatom case, the dipole-induced dipole C6 coefficients have been calculated for various diatomic distances up to 15 Å. The distance dependence of their isotropic C6000 and anisotropic C6202 components has been fitted to an analytical form similar to that used for the static dipole polarizabilities of the diatomics

First-principles study of stability, band structure, and optical properties of the ordered Ge \u3c inf\u3e 0.50 Sn \u3c inf\u3e 0.50 alloy

All electron density functional theory calculations were performed on the ordered Ge0.50Sn0.50 alloy in the zinc-blende phase to study its structural, electronic, and optical properties along with its stability with respect to the elemental components. We employed a linear combination of atomic orbitals approach for calculations in which the Bloch functions were constructed as linear combinations of atom-centered Gaussian orbitals. The calculated results show a relative stability of the GeSn alloy in the zinc-blende phase for which the lattice constant and bulk modulus are predicted to be 6.20 Å and 53 GPa, respectively. Analysis of band structure and density of states shows the cubic-ordered alloy to be a direct-gap semiconductor with a small band gap. The optical properties, such as dielectric constant and plasmon energy of the cubic alloy, appear to be about the average of the respective values in its elemental components. © 1999 American Institute of Physics

Ab initio calculation of the nonlinear susceptibility χ(2) of a crystal surface.

International audienceThe polarizability and 1st hyperpolarizability of a crystal surface were calcd. from a sum over states method using cryst. orbitals of the CRYSTAL program. The linear and nonlinear optical properties of the (001) LiF surfaces are evaluated layer by layer, showing that the response of inner layers to an elec. field tends effectively to the bulk response value while the χ(2) susceptibility components responsible of 2nd harmonic generation (SHG) are no longer equal to zero at the surface of the crystal

Efficacité des semiconducteurs utilisés en photovoltaïque et en photocatalyse Une analyse fondée sur la DFT

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First-principles calculations of nonlinear optical susceptibility of inorganic materials

A method for calculations of the frequency-dependent nonlinear susceptibility of inorganic materials is implemented in the velocity gauge using a linear combination of atomic orbitals (LCAO) method within the framework of either the Hartree-Fock approximation or density functional theory. It is based on the standard time-dependent diagrammatic perturbation theory and has previously been applied successfully for atoms and molecules. For inorganic materials, it requires the eigenvalues and position operator matrix elements at several k points in the Brillouin zone. A quantitative assessment of the predictability of the method was made on cubic GaN for which the results of previous theoretical studies are available

Water Adsorption on MgO Surfaces: A Vibrational Analysis

Using DFT calculations, we have considered different adsorption configurations of water molecules on MgO surfaces. In some cases, we have observed a chemical reaction between water and the surface, with the formation of hydroxyl groups. We have systematically compared the calculated Raman spectra of the final optimized structures with the measured spectra from MgO nanoparticles. Our results confirm the high reactivity of MgO surfaces with water. Some obtained structures can be considered precursors for the transformation of MgO into Mg(OH)2. We suggest that some of them could be identified using Raman spectroscopy. Our study confirms the high potentiality of Raman spectroscopy, associated with numerical calculations, for the study of chemical reactivity of nanoparticles

Implementation of the finite field perturbation method in the CRYSTAL program for calculating the dielectric constant of periodic systems

cited By 45International audienceThe finite field approach has been implemented in the periodic ab initio CRYSTAL program and been used for calculating the dielectric constants of crystalline LiF and MgO (FCC structure) and BeO (wurtzite structure). To maintain the periodicity along the applied field direction, a "sawtooth" potential is used in conjunction with a supercell scheme. Supercells four to five times longer than the primitive cell in the direction of the applied field provide well-converged results. The influence of the computational parameters is discussed. An alternative scheme has also been implemented, for inner check, that consists of applying a static electric field to a slab of increasing thickness in the direction orthogonal to the surface; the dielectric response at the center of the slab is shown to converge rapidly to the bulk value evaluated with the sawtooth field. The method is accurate and permits the determination of nonlinear corrections to the dielectric constant. When used in conjunction with the local density approximation (LDA) scheme, it provides for the dielectric constant of the three above-mentioned compounds values close to those recently obtained with a time-dependent density functional theory approach