Structural, Electronic, Magnetic and Mechanical Properties and Magnetocaloric Effect of the Full-Heusler Co2MnGa

Structural, electronic, magnetic and mechanical properties of the Co2MnGa have been calculated with functional density theory using full potential linear augmented plane wave method as implemented in the Wien2k code. Exchange correlation effects for these properties are treated by generalized gradient approximation while for electronic and magnetic properties, in addition to (WC-GGA) correction, mBJ-GGA scheme was also applied. The stiffness constant of the spin wave and the Curie temperature are calculated. Moreover, mechanical parameters included three elastic constants, compression modulus, Young’s modulus and shear modulus are also investigated. This theoretical study provides detailed information on the compound Co2MnGa, in different aspects and can also provide information on the application of this material. Obtained data from ab initio calculations are used as input for Monte Carlo simulations to study the magnetic properties and magnetocaloric effect. Transition temperature, magnetic entropy change, adiabatic temperature change and relative cooling power were found.

First-Principles Investigation of structural, Optical, and Electrical properties of MgO Nanocrystals

Nanocrystal interfaces can strongly influence the optical and electrical properties and charging trapping phenomena observed on oxide nanocrystal ensembles. The well-defined shape and controllable size distributions of MgO nanocrystals are a convenient system for studying these effects. Therefore, in the present work focused on the effect of temperature on the optical and electrical properties of magnesium oxide (MgO) nanocrystals, together with the responsible atomic centers, the bulk MgO is a study based on the first principle functional density theory (DFT) using PBE-GGA approximations. The absorption coefficient shows that MgO shows good coverage in the ultraviolet range. The bulk MgO is a direct bandgap nanocrystal at G point in the Brillion Zone despite the temperature applied values. The temperature is applied to alter the bandgap pattern and closes the bandgap at a high temperature. The PDOS and imaginary part of the dielectric function further confirm the insulator properties of the observed bandgap. Our results show that the optical properties are affected by the inconsistent temperature manners despite the different temperatures given to the system. Our absorption curve confirms that the nanocrystal is a good candidate for ultraviolet device application with a significantly high reflectivity percentage.

Properties Evaluation of Fe95-xSi5Nix Under the Earth's Inner-Core Conditions: Insight from the Ab-Initio Investigation

In this article we investigate under the same Earth's core conditions, the structural, electronic, and transport properties of Fe-Si-Ni ternary alloys based on Fe and 5% of Si with various concentrations 0%, 15%, 25%, and 40% of element Ni, by means of First-principles calculations. Based on Functional Density Theory (DFT). The Local Density Approximation (LDA) also has been adopted for the potential exchange correlation. We perform the calculation of electronic property at 360 GPa using the software Akai-KKR (machikaneyama), which used the Korringa-Kohn-Rostoker method along with coherent potential approximation (KKR-CPA). Afterward, we calculate the electrical resistivity of impurities formed on the Kubo-Greenwood formula with the vertex correction using SPR-KKR code, which is based on the relativistic polarized spin method. Then, we model the thermal conductivity by electrical resistivity for both varying in the range of 320–360 GPa and 4500-6000k of pressure and temperature, respectively; according to the conditions of the Earth’s inner core ICB using Wiedemann-Franz law. Hence, our results suggest that 85–115 µΩ·cm at 0 K and 320–360 GPa, then 225–285 µΩ·cm at 4500–6000 K and 360 GPa for electrical resistivity, and then 45–55 W·m− 1·K− 1 at 4500–6000 K and 360 GPa of thermal conductivity of Earth’s inner core. Lastly, the thermal and compositional convection is one of the major factors of global magnetic field that is generated by geodynamo driven.

PROPIEDADES ESTRUCTURALES, MAGNÉTICAS E HIPERFINAS DE LA FERRITA MgFe2O4: ESTUDIO MEDIANTE CÁLCULOS AB-INITIO

We present here a first principles study of the structural, electronic, magnetic, and hyperfine properties of magnesium ferrite, MgFe2O4 (spinel structure). The study was carried out within the framework of Functional Density Theory (DFT) using the full potential linearized augmented plane waves method (FPLAPW) using both the Generalized Gradient (GGA) and the GGA+U approximations for the exchange and correlation potential. To discuss the magnetic ordering and the lowest energy structure of the system we consider different distributions of Mg and Fe ions in both cationic sites of the spinel structure, as well as different spin configurations. Our calculations predict that the equilibrium structure corresponds to an inverted antiferromagnetic configuration, in which the magnetic moments of the Fe atoms located at sites A are ferromagnetically ordered among themselves and antiferromagnetically with respect to the Fe located at the sublattice of sites B. Our GGA calculations underestimate the energy band-gap of the system, while GGA+U predict a band-gap of 2.3 eV, in excellent agreement with the reported values. The results for the hyperfine properties at the Fe sites (isomer shift, quadrupole splitting and hyperfine field) are in excellent agreement with the Mössbauer spectroscopy results reported in the literature, giving support to the equilibrium structure predicted by FP-LAPW.

Graphene: Insights on Biological, Radiochemical and Ecotoxicological Aspects

Graphene, including graphene quantum dots, its oxide and unoxidized forms (pure graphene) have several properties, like fluorescence, electrical conductivity, theoretical surface area, low toxicity, and high biocompatibility. In this study, we evaluated genotoxicity (in silico analysis using the functional density theory-FDT), cytotoxicity (human glioblastoma cell line), in vivo pharmacokinetics, in vivo impact on microcirculation and cell internalization assay. It was also radiolabeled with lutetium 177 (177Lu), a beta emitter radioisotope to explore its therapeutic use as nanodrug. Finally, the impact of its disposal in the environment was analyzed using ecotoxicological evaluation. FDT analysis demonstrated that graphene can construct covalent and non-covalent bonds with different nucleobases, and graphene oxide is responsible for generation of reactive oxygen species (ROS), corroborating its genotoxicity. On the other hand, non-cytotoxic effect on glioblastoma cells could be demonstrated. The pharmacokinetics analysis showed high plasmatic concentration and clearance. Topical application of 0.1 and 1 mg/kg of graphene nanoparticles on the hamster skinfold preparation did not show inflammatory effect. The cell internalization assay showed that 1-hour post contact with cells, graphene can cross the plasmatic membrane and accumulate in the cytoplasm. Radio labeling with 177Lu is possible and its use as therapeutic nanosystem is viable. Finally, the ecotoxicity analysis showed that A. silina exposed to graphene showed pronounced uptake and absorption in the nauplii gut and formation of ROS. The data obtained showed that although being formed exclusively of carbon and carbon-oxygen, graphene and graphene oxide respectively generate somewhat contradictory results and more studies should be performed to certify the safety use of this nanoplatform.

A DFT study of structural and electronic properties of anatase TiO2 phase with Ni and oxygen vacancies impurities

In the present work, first-principle theory using the functional density theory (DFT) was used in the ABINIT software package using the PBE pseudopotential (norm-conserving pseudopotentials). To determine the structural parameters such as lattice constant, Bulk modules, and energy formation, for the TiO2 anatase phase doped with substitutional and interstitial nickel impurity, oxygen vacancies (VO) are also included in the present work. For this study, the 2x1x1 supercells with 24 atoms and 2x2x1 with 48 atoms were used. Different types of Ni dopants and oxygen vacancies were considered for energy formation using the 2x2x1 supercell. Our results show that the values of network parameters, minimum energy, and Bulk modulus remain constant with the supercell's growth. With the inclusion of Ni in the supercell substituting the Ti-ions, the unit cell volume (V) exhibits a decrease in agreement with ionic radii mismatch between Ti and Ni atoms. However, when entry as an interstitial form a significant increase is shown. The preliminary results of the energy of formation analyzed for the Ni defects show that it is more probable for an interstitial Ni than for a substitutional Ni.

Heats of Formation for Iodine Compounds: A DFT Study

The heat formation of 33 molecules for the iodine compounds were performed using the functional density theory (DFT) (B3LYP, M06-2X and WB97XD), and the basis sets (6-311G (d, p) and cc-pVQZ + d). The best agreement with experimental data was achieved by using B3LYP/cc-pVQZ+d, WB97XD/6-311G (d,p) and MP2/6-311G (d,p).

A DFT study of structural and electronic properties of anatase TiO2 phase with Ni and oxygen vacancies impurities

In the present work, first-principle theory using the functional density theory (DFT) was used in the ABINIT software package using the PBE pseudopotential (norm-conserving pseudopotentials). To determine the structural parameters such as lattice constant, Bulk modules, and energy formation, for the TiO2 anatase phase doped with substitutional and interstitial nickel impurity, oxygen vacancies (VO) are also included in the present work. For this study, the 2x1x1 supercells with 24 atoms and 2x2x1 with 48 atoms were used. Different types of Ni dopants and oxygen vacancies were considered for energy formation using the 2x2x1 supercell. Our results show that the values of network parameters, minimum energy, and Bulk modulus remain constant with the supercell's growth. With the inclusion of Ni in the supercell substituting the Ti-ions, the unit cell volume (V) exhibits a decrease in agreement with ionic radii mismatch between Ti and Ni atoms. However, when entry as an interstitial form a significant increase is shown. The preliminary results of the energy of formation analyzed for the Ni defects show that it is more probable for an interstitial Ni than for a substitutional Ni.

Activated Carbon from Rice Husk Biochar with High Surface Area

Activated carbons derived from rice husk pyrolysis (biochar) were prepared by chemical activation at different biochar/K2CO3 proportions in order to assess its capacity as adsorbent. The activated material was characterized by X-ray diffraction (DRX), Raman spectroscopy, scanning electron microscopy (SEM), the Brunauer, Emmet, and Teller (BET) method. The Barret, Joyner, and Halenda (BJH) method and functional density theory (DFT), presenting interesting texture properties, such as high surface area (BET 1850 m2 g-1) and microporosity, which allow its use as a sorbent phase in solid-phase extraction (SPE) of the main constituents of the aqueous pyrolysis phase. It was demonstrated that the activated carbon (RH-AC) adsorbs different compounds present in from rice husk pyrolysis wastewater through quantitative analysis by high-performance liquid chromatography with a diode-array detector (HPLC-DAD), presenting good linearity (R2 > 0.996) at 280 nm.