Investigation of Origanum libanoticum Essential Oils Chemical Polymorphism by Independent Components Analysis (ICA)

International audienceThe essential oils obtained from Origanum libanoticum Boiss., a plant endemic to Lebanon, were analyzed by GC/MS. Seventy compounds were identified, covering till 99.8% of the total oil composition. All samples were p-cymene and/or β-caryophyllene chemotype, with variable percentage of other compounds such as α-pinene, myrcene, α-phellandrene, limonene, etc. Compared to traditional drying method, lyophilized samples provided the highest essential oil (EO) yields and yields were higher at flowering stage (Chouwen: 0.33% in 2013 and 0.32% in 2014; Qartaba: 0.27% in 2013 and 0.37% in 2014). According to independent components analysis (ICA), date and site of harvest, altitude and drying technique had no effect on the variation of O. libanoticum EO chemical composition. An annual variation of EOs composition was observed since a particular variation in some major components concentration was revealed monthly and annually between 2013 and 2014

Ab initio investigations of the Ca₂IrO₄-type structure as a "post-K₂NiF₄": Case study of Na₂OsO₄

Deriving the energy-volume equation of state for Na2OsO4 in its actual Ca2IrO4-type structure at high pressure and in hypothetic K2NiF4-type, leads to energy destabilization at a larger volume for the latter and to propose the former as a post-K2NiF4 through which a tuning of the magnetism and conductivity can be achieved: while the oxide system is magnetically silent in Ca2IrO4-type due to spin pairing (S = 0 for d2 Os6+) with a semi-conducting behavior, a finite moment develops in the latter when spin polarization is accounted for (S = 1)

Electronic structure and chemical bonding of LiYSi

The electronic structure of the ternary silicide LiYSi (ZrNiAl type, P62m N°189, a = 702.3, c = 421.2 pm) is examined from ab initio with an assessment of the properties of chemical bonding. The compound is found semi-conducting with a very small gap and the chemical bonding is found mainly between Y and Si as well as Li-Si with differentiated Li-Si1/Li-Si2. The structure with totally de-intercalated Li keeps the characteristics of LiYSi with a reduction of the c/a ratio and of the volume albeit with less stability than binary YSi with orthorhombic CrB type structure. The electronic structure calculations indicate the possibility of an at least partial delithiation Li1−xYSi while keeping the hexagonal structure

Hydrogen insertion effects on the electronic structure of equiatomic MgNi traced by ab initio calculations

For equiatomic MgNi which can be hydrogenated up to the composition MgNiH1.6 at an absorption/desorption temperature of 200 °C, the effects of hydrogen absorption are approached with the model structures MgNiH, MgNiH2 and MgNiH3. From full geometry optimization and calculated cohesive energies obtained within DFT, the MgNiH2 composition close to the experimental limit is identified as most stable. Charge density analysis shows an increasingly covalent character of hydrogen: MgNiH (H−0.67) → MgNiH2 (H−0.63) → MgNiH3 (H−0.55). While Mg-Ni bonding prevails in MgNi and hydrogenated model phases, extra itinerant low-energy Ni states appear when hydrogen is introduced signaling Ni-H bonding which prevails over Mg-H as evidenced from total energy calculations and chemical bonding analyses

Hydrogen insertion effects on the electronic structure of equiatomic MgNi traced by ab initio calculations

For equiatomic MgNi which can be hydrogenated up to the composition MgNiH1.6 at an absorption/desorption temperature of 200 °C, the effects of hydrogen absorption are approached with the model structures MgNiH, MgNiH2 and MgNiH3. From full geometry optimization and calculated cohesive energies obtained within DFT, the MgNiH2 composition close to the experimental limit is identified as most stable. Charge density analysis shows an increasingly covalent character of hydrogen: MgNiH (H−0.67) → MgNiH2 (H−0.63) → MgNiH3 (H−0.55). While Mg-Ni bonding prevails in MgNi and hydrogenated model phases, extra itinerant low-energy Ni states appear when hydrogen is introduced signaling Ni-H bonding which prevails over Mg-H as evidenced from total energy calculations and chemical bonding analyses

Nickel induced iono-covalent character of hydrogen in RbMgH3 from first principles

The large ionic character in hexagonal perovskite RbMgH3 is reduced by selective substitutions by Ni followed by full geometry optimization within DFT leading to preserve the structure and symmetry of the pristine hydride. From the Bader charge analysis, an increasingly iono-covalent character is introduced with larger amounts of Ni substituting to Mg. For the Ni rich composition RbMg1/3Ni2/3H3, found most stable from cohesive energies, the charge on H decreases down to −0.2. This peculiar behavior should enable enhancing the kinetics of H release for potential applications

Ab initio study of MgH2: Destabilizing effects of selective substitutions by transition metals

The strong ionicity of H within rutile MgH2 is reduced by selective substitution of Mg by T (=Fe, Co, Ni, Pd, Pt) using trirutile super-structure host TMg2H6. These novel model systems, as computed in the quantum mechanical framework of density functional theory, showed a gradual decrease of the charges carried by H down to −0.02e improving the use of MgH2 for applications

Changes in electronic, magnetic and bonding properties from Zr2FeH5 to Zr3FeH7 addressed from ab initio

Potential hydrogen storage ternaries Zr3FeH7 and Zr2FeH5, are studied from ab initio with the purpose of identifying changes in electronic structures and bonding properties. Cohesive energy trends: Ecoh. (ZrH2) > Ecoh. (Zr2FeH5) > Ecoh. (Zr3FeH7) > Ecoh. (hypothetic-FeH) indicate a progressive destabilization of the binary hydride ZrH2 through adjoined Fe so that Zr3FeH7 is found less cohesive than Zr2FeH5. From the energy volume equations of states EOS the volume increase upon hydriding the intermetallics leads to higher bulk moduli B0 explained by the Zr/Fe-H bonding. Fe-H bond in Zr2FeH5 leads to annihilate magnetic polarization on Fe whereas Fe magnetic moment develops in Zr3FeH7 identified as ferromagnetic in the ground state. These differences in magnetic behaviors are due to the weakly ferromagnetic Fe largely affected by lattice environment, as opposed to strongly ferromagnetic Co. Hydrogenation of the binary intermetallics weakens the inter-metal bonding and favors the metal-hydrogen bonds leading to more cohesive hydrides as with respect to the pristine binaries. Charge analyses point to covalent like Fe versus ionic Zr and hydrogen charges ranging from covalent H−0.27 to more ionic H−0.5

Drastic changes of electronic structure, bonding properties and crystal symmetry in Zr2Cu by hydrogenation, from ab initio

Gradual hydrogen uptake into Zr2Cu intermetallic leads to crystal symmetry changes from tetragonal Zr2CuH2 to monoclinic Zr2CuH5. This experimental finding is explained here from cohesive energies computed within quantum DFT for Zr2CuHx (x = 1, 2, 3, 4, 5) models in both structures. The threshold is found at 2 < x < 3 in agreement with experiment. Beside structural crossover, electronic properties, chemical bonding, and mechanical behavior are also analyzed. Metal-H interactions arising from increasingly H presence in Zr2Cu lead to more and most cohesive and harder Zr2CuH2 and Zr2CuH5 respectively

Ab initio investigations of the electronic structure and chemical bonding of Li2ZrN2

The electronicstructure of the ternary nitride Li2ZrN2 is examined from abinitio with DFT computations for an assessment of the properties of chemicalbonding. The compound is found insulating with 1.8 eV band gap; it becomes metallic and less ionic upon removal of one equivalent of Li. The chemical interaction is found mainly between Zr and N on one hand and Li and N on the other hand. While all pair interactions are bonding, antibonding N-N interactions are found dominant at the top of the valence band of Li2ZrN2 and they become less intense upon removal of Li. From energy differences the partial delithiation leading to Li2−xZrN2 (x=∼1) is favored