{\it Ab initio} calculations of magnetic structure and lattice dynamics of Fe/Pt multilayers

The magnetization distribution, its energetic characterization by the interlayer coupling constants and lattice dynamics of (001)-oriented Fe/Pt multilayers are investigated using density functional theory combined with the direct method to determine phonon frequencies. It is found that ferromagnetic order between consecutive Fe layers is favoured, with the enhanced magnetic moments at the interface. The bilinear and biquadratic coupling coefficients between Fe layers are shown to saturate fast with increasing thickness of nonmagnetic Pt layers which separate them. The phonon calculations demonstrate a rather strong dependence of partial iron phonon densities of states on the actual position of Fe monolayer in the multilayer structure.Comment: 7 pages, 8 figure

Influence of anharmonicity on the negative thermal expansion of α−Sn\alpha-Sn

The lattice vibrational properties of $\alpha-Sn$ (gray tin) were investigated experimentally by temperature-dependent x-ray diffraction and theoretically by density functional theory calculations. Similar to the other elements of group IV, $\alpha-Sn$ exhibits a lattice anomaly at low temperatures and negative thermal expansion, with a minimum at $\sim 27K$ and a magnitude three times larger than in Si. The influence of anharmonic effects up to fourth-order potential terms on the phonon dispersion relations, the lattice parameters, and the thermal expansion coefficient have been tested. The performed analysis gives an excellent agreement with experiment when quartic potential terms are included in the theory. We point out that negative thermal expansion in $\alpha-Sn$ is not driven by the anharmonicity of the interatomic potential. This resolves the long-standing puzzle in the thermal behavior of $\alpha-Sn$

Ab initio and nuclear inelastic scattering studies of Fe3_3Si/GaAs heterostructures

The structure and dynamical properties of the Fe$_3$Si/GaAs(001) interface are investigated by density functional theory and nuclear inelastic scattering measurements. The stability of four different atomic configurations of the Fe$_3$Si/GaAs multilayers is analyzed by calculating the formation energies and phonon dispersion curves. The differences in charge density, magnetization, and electronic density of states between the configurations are examined. Our calculations unveil that magnetic moments of the Fe atoms tend to align in a plane parallel to the interface, along the [110] direction of the Fe$_3$Si crystallographic unit cell. In some configurations, the spin polarization of interface layers is larger than that of bulk Fe$_3$Si. The effect of the interface on element-specific and layer-resolved phonon density of states is discussed. The Fe-partial phonon density of states measured for the Fe$_3$Si layer thickness of three monolayers is compared with theoretical results obtained for each interface atomic configuration. The best agreement is found for one of the configurations with a mixed Fe-Si interface layer, which reproduces the anomalous enhancement of the phonon density of states below 10 meVComment: 14 pages, 9 figures, 4 table

Structure and elastic properties of Mg(OH)2_2 from density functional theory

The structure, lattice dynamics and mechanical properties of the magnesium hydroxide have been investigated with static density functional theory calculations as well as \it {ab initio} molecular dynamics. The hypothesis of a superstructure existing in the lattice formed by the hydrogen atoms has been tested. The elastic constants of the material have been calculated with static deformations approach and are in fair agreement with the experimental data. The hydrogen subsystem structure exhibits signs of disordered behaviour while maintaining correlations between angular positions of neighbouring atoms. We establish that the essential angular correlations between hydrogen positions are maintained to the temperature of at least 150 K and show that they are well described by a physically motivated probabilistic model. The rotational degree of freedom appears to be decoupled from the lattice directions above 30K

Lattice dynamics of endotaxial silicide nanowires

Self-organized silicide nanowires are considered as main building blocks of future nanoelectronics and have been intensively investigated. In nanostructures, the lattice vibrational waves (phonons) deviate drastically from those in bulk crystals, which gives rise to anomalies in thermodynamic, elastic, electronic, and magnetic properties. Hence, a thorough understanding of the physical properties of these materials requires a comprehensive investigation of the lattice dynamics as a function of the nanowire size. We performed a systematic lattice dynamics study of endotaxial FeSi$_2$ nanowires, forming the metastable, surface-stabilized $\alpha$-phase, which are in-plane embedded into the Si(110) surface. The average widths of the nanowires ranged from 24 to 3 nm, their lengths ranged from several $\mu$m to about 100 nm. The Fe-partial phonon density of states, obtained by nuclear inelastic scattering, exhibits a broadening of the spectral features with decreasing nanowire width. The experimental data obtained along and across the nanowires unveiled a pronounced vibrational anisotropy that originates from the specific orientation of the tetragonal $\alpha$-FeSi$_2$ unit cell on the Si(110) surface. The results from first-principles calculations are fully consistent with the experimental data and allow for a comprehensive understanding of the lattice dynamics of endotaxial silicide nanowires.Comment: 9 pages, 7 figures, 3 table

Enrichment of food with long-chain omega-3 fatty acids

Nowoczesna żywność ma nie tylko dostarczać energii, ale również poprawiać lub podtrzymywać dobry stan zdrowia. Przykładem może być żywność wzbogacona długołańcuchowymi wielonienasyconymi kwasami tłuszczowymi (LC PUFA) z rodziny omega-3, szczególnie kwasem dokozaheksaenowym (DHA) oraz eikozapentaenowym (EPA). Kwasy te bardzo korzystnie oddziałują na układ krążenia oraz nerwowy. Niestety ich wytwarzanie w organizmie zachodzi z niewielką wydajnością. Dlatego głównym źródłem LC PUFA powinna być spożywana żywność. Najbogatsze w te dobroczynne kwasy są ryby i inne organizmy morskie, które niestety w większości krajów z tzw. zachodnim typem diety, w tym w Polsce, nie są spożywane w dostatecznej ilości. Dla uzupełnienia niedoborów można stosować suplementy diety oraz żywność wzbogaconą w omega-3. Wytwarzanie żywności z dodatkiem oleju rybiego wymaga pokonania wielu trudności technologicznych, przede wszystkim związanych z występowaniem "rybiego" posmaku i zapachu, a także z ochroną wielonienasyconych kwasów przed utlenianiem. Możliwym sposobem rozwiązania tych problemów jest dodawanie do żywności oleju rybiego w formie mikrokapsułek. Do enkapsulacji olejów bogatych w omega-3 LC PUFA stosuje sie takie metody, jak: suszenie rozpyłowe, ekstruzję i koacerwację. Dla osiągnięcia jak najlepszej stabilności oksydatywnej LC PUFA istotny jest również odpowiedni dobór materiałów osłonkowych do mikrokapsułkowania. Zastosowanie substancji odpornych na trawienie w górnym odcinku przewodu pokarmowego stwarza nadzieje na kontrolowane dostarczanie kwasów omega-3 do jelita grubego.Modern food is intended not only to produce energy, but also to improve or maintain good health. Food enriched with long-chain omega-3 polyunsaturated fatty acids (LC PUFAs), particularly docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) can be an example. These acids favorably affect cardiovascular and nervous systems. Unfortunately, their production in the body occurs at low efficiency. Therefore, the main source of LC PUFAs should be ingested food. Fish and other marine organisms are the richest source of these beneficial fatty acids. Unfortunately, in most countries with the so-called western type diet, including Poland, they are not consumed in sufficient quantity. Food supplements and food enriched with omega-3 fatty acids may be used to complete their deficiency. Manufacture of food with fish oil addition requires overcoming many technological difficulties, primarily associated with the occurrence of "fish" taste and smell, as well as the protection of polyunsaturated acids against oxidation. The addition of microencapsulated fish oil to food is a possible way to solve these problems. For the encapsulation of oil rich in omega-3 LC PUFAs such methods as spray-drying, extrusion and coacervation were used. To achieve the best oxidative stability of LC PUFAs, an appropriate choice of wall material is also crucial. The use of substances resistant to digestion in the upper part of gastrointestinal tract creates hope for the controlled delivery of omega-3 to the large intestine

Ab initio lattice dynamics and elastic constants of ZrC

Ab initio calculations and a direct method are applied to derive the phonon dispersion relations and phonon density of states for the ZrC crystal. The results are in good agreement with neutron scattering data. The force constants are determined from the Hellmann-Feynman forces induced by atomic displacements in a 2 supercell. The elastic constants are found using the deformation method and successfully compare with experimental data