The theoretical DFT study of electronic structure of thin Si/SiO2 quantum nanodots and nanowires

The atomic and electronic structure of a set of proposed thin (1.6 nm in diameter) silicon/silica quantum nanodots and nanowires with narrow interface, as well as parent metastable silicon structures (1.2 nm in diameter), was studied in cluster and PBC approaches using B3LYP/6-31G* and PW PP LDA approximations. The total density of states (TDOS) of the smallest quasispherical silicon quantum dot (Si85) corresponds well to the TDOS of the bulk silicon. The elongated silicon nanodots and 1D nanowires demonstrate the metallic nature of the electronic structure. The surface oxidized layer opens the bandgap in the TDOS of the Si/SiO2 species. The top of the valence band and the bottom of conductivity band of the particles are formed by the silicon core derived states. The energy width of the bandgap is determined by the length of the Si/SiO2 clusters and demonstrates inverse dependence upon the size of the nanostructures. The theoretical data describes the size confinement effect in photoluminescence spectra of the silica embedded nanocrystalline silicon with high accuracy.Comment: 22 pages, 5 figures, 1 tabl

Комплекс цефтриаксона с Mg(II): синтез, структура, спектральные и антибактериальные свойства

Magnesium complex of ceftriaxone was obtained and characterized by atomic-emission and elemental analysis, TGA, FTIR and Raman spectroscopy, X‑ray diffraction and density functional theory calculations. Ceftriaxone was coordinated to the magnesium ion by the oxygen of the triazine cycle in the 6th position, the nitrogen of the amine group of the thiazole ring, and oxygen atoms of the lactam carbonyl and carboxylate groups. The disodium salt of ceftriaxone and magnesium complex were screened for antibacterial activity against Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosaПолучен и охарактеризован магниевый комплекс цефтриаксона методами атомно-эмиссионного и элементного анализов, ТГА, ИК- и КР‑спектроскопии, РФА и расчетов теории функционала плотности. Цефтриаксон координируется к иону магния через кислород триазинового цикла в шестом положении, азот аминогруппы тиазольного цикла и атомы кислорода карбоксильной и лактамной групп. Динатриевая соль цефтриаксона и комплекс магния были исследованы на антибактериальную активность в отношении Staphylococcus aureus, Escherichia coli и Pseudomonas aeruginos

The influence of size effect on the electronic and elastic properties of diamond films with nanometer thickness

The atomic structure and physical properties of few-layered oriented diamond nanocrystals (diamanes), covered by hydrogen atoms from both sides are studied using electronic band structure calculations. It was shown that energy stability linear increases upon increasing of the thickness of proposed structures. All 2D carbon films display direct dielectric band gaps with nonlinear quantum confinement response upon the thickness. Elastic properties of diamanes reveal complex dependence upon increasing of the number of layers. All theoretical results were compared with available experimental data.Comment: 16 pages, 5 figures, 3 table

Two-Dimensional Lattices of VN: Emergence of Ferromagnetism and Half-Metallicity on Nanoscale

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.Two-dimensional (2D) ferromagnets with high spin-polarization ratio and high Curie temperature are crucial for developing next-generation spintronic nanodevices. Using first-principles calculations, we predict two polymorphic modifications (t-VN and h-VN) of 2D VN lattices that have robust intrinsic ferromagnetic properties and high Curie temperatures. Whereas t-VN has 99.9% of spin polarization at the Fermi level, h-VN possesses a half-metallic type of conductivity and keeps it after contact with semiconducting MoS2, which can be used as the substrate for h-VN synthesis and valley polarized contacts. Magnetocrystalline anisotropy energy of 2D VN polymorphs is found to be at least an order larger than those of Fe and Ni bulks. The phonon spectra and ab initio molecular dynamic simulation prove that 2D VN lattices have a high thermodynamic stability. These advantages demonstrate that the VN monolayers should be promising candidates for low-dimensional spintronic devices

Quantum Chemical Study of Atomic Structure and Spin States of the Cox(C60)n (x=1-8, n=1-3) Complex Nanoclusters

The main features of the local atomic structure of novel Con(C60)x (n=1-8, x=1-3) complexes and Con clusters as well were studied using the ab initio GGA calculations for a set of low and high energy isomers in different spin states. It is shown that high-spin low-symmetry structure of free-standing Con clusters is determined by Jahn-Teller distortions. For the Co(C60)x (x=1-3) isomers the spin state S=1/2 is energetically preferable whereas the low energy isomers of Co2(C60)x (x=1-3) have an intermediate spin state of S=1. The η2 (6-6 edge of C60) type of cobalt ion coordination is preferable for both n=1 and n=2 cases. The η2 (coordination with 6-5 edge) and even the η5 (C5 fragment) types serve as low and high energy intermediates for the cobalt ions migration around the C60 cage. Formation of cobalt dimers can be the final stage of evolution of Con(C60)x atomic structure approaching the equilibrium atomic geometry. For higher n (3-8) the formation of η2, η2 or η1 coordination bonds between Con fragment and C60 molecules through carbon hexagons results in stable complex nanoclusters with nonmonotonic change of average spin momentum upon the number of cobalt atoms in the Con cores. The theoretical results are compared with corresponding experimental data

Strong Electron Correlations Determine the Stability and Properties of Er-doped Silicon Quantum Dots

С помощью теории функционала плотности (DFT) в работе проводилось изучение электронной структуры кремниевых квантовых точек Голдберговского типа с центральными симметрическими пустотами и их эндоэдральными комплексами с эрбием. После оптимизации структуры с помощью DFT-метода был проведен расчет экспериментальных свойств Er-допированного нанокристаллического кремния. Кроме того, исследования позволили объяснить роль симметрии центральных пустот в квантовых точках и провести интерпретацию особенностей в плотностях состояний.The electronic structure of the Goldberg silicon quantum dots with central symmetric hollows and their endohedral complexes with erbium was studied using DFT with and without the strong electron correlations, whose inclusion was found to determine the binding energy. Based on optimized DFT structures, we were able to explain the details of Er-doped nanocrystalline silicon made in experiment. The role of symmetry of the central hollows in quantum dots was elucidated, and the key features of the density of states are explained, providing information for the tuning and design of Er-doped silicon light emitters

Two-Dimensional Lattices of VN: Emergence of Ferromagnetism and Half-Metallicity on Nanoscale

Two-dimensional (2D) ferromagnets with high spin-polarization ratio and high Curie temperature are crucial for developing next-generation spintronic nanodevices. Using first-principles calculations, we predict two polymorphic modifications (<i>t</i>-VN and <i>h</i>-VN) of 2D VN lattices that have robust intrinsic ferromagnetic properties and high Curie temperatures. Whereas <i>t</i>-VN has 99.9% of spin polarization at the Fermi level, <i>h</i>-VN possesses a half-metallic type of conductivity and keeps it after contact with semiconducting MoS₂, which can be used as the substrate for <i>h</i>-VN synthesis and valley polarized contacts. Magnetocrystalline anisotropy energy of 2D VN polymorphs is found to be at least an order larger than those of Fe and Ni bulks. The phonon spectra and ab initio molecular dynamic simulation prove that 2D VN lattices have a high thermodynamic stability. These advantages demonstrate that the VN monolayers should be promising candidates for low-dimensional spintronic devices

Theoretical Investigation of the Prospect to Tailor ZnO Electronic Properties with VP Thin Films

The atomic and electronic structure of vanadium phosphide one- to four-atomic-layer thin films and their composites with zinc oxide substrate are modelled by means of quantum chemistry. Favorable vanadium phosphide to ZnO orientation is defined and found to remain the same for all the structures under consideration. The electronic structure of the composites is analyzed in detail. The features of the charge and spin density distribution are discussed

Ni-modification of al (III) Surface and use it as Hydrogen Storage Material

В данной работе проводилось теоретическое исследование допированной никелем поверхности алюминия, которое было выполнено в рамках теории функционала плотности (DFT) с использованием обобщенного градиентного приближения GGA-PBE. Была изучена электронная структура при взаимодействии поверхности алюминия с атомами никеля. Используя метод NEB, рассчитали барьер для диффузии атома никеля по поверхности алюминия и с поверхности в приповерхностный слой. Показано, что атомам никеля предпочтительнее замещать атомы алюминия в приповерхностных слоях, что впоследствии приводит к образованию интерметаллида Al3Ni. Данная фаза была исследована на возможность сорбции водорода. Результаты показали, что при нормальных условиях водороду не свойственно содержаться в данной фазеIn this paper, a theoretical study of the nickel -doped of aluminum surface was carried in the framework of density functional theory (DFT) using the generalized gradient approximation GGA-PBE. The electronic structure of interface Al(III) surface and nickel atoms was investigated. Using the method of NEB, the diffusion barrier of the nickel atom from the surface into the subsurface layer was calculated. It values shows that the nickel atom is preferable to replace aluminum atom in the subsurface layer, which subsequently leads to the formation of intermetallic Al3Ni. This phase has been investigated the possibility of hydrogen sorption. The results showed that the hydrogen is not typical contained in this phase under normal condition