Search Results

1 - 10 of 28 items :

  • "ab initio calculations" x
Clear All
Ab initio calculations of structural, elastic, electronic and thermodynamic properties of the cerium filled skutterudite CeRu4P12 under the effect of pressure

Abstract

The paper presents an investigation on crystalline, elastic and electronic structure in addition to the thermodynamic properties for a CeRu4P12 filled skutterudite device by using the full-potential linear muffin-tin orbital (FP-LMTO) method within the generalized gradient approximations (GGA) in the frame of density functional theory (DFT). For this purpose, the structural properties, such as the equilibrium lattice parameter, bulk modulus and pressure derivatives of the bulk modulus, were computed. By using the total energy variation as a function of strain we have determined the independent elastic constants and their pressure dependence. Additionally, the effect of pressure P and temperature T on the lattice parameters, bulk modulus, thermal expansion coefficient, Debye temperature and the heat capacity for CeRu4P12 compound were investigated taking into consideration the quasi-harmonic Debye model.

Open access
Structural properties of hypothetical CeBa2Cu3O7 compound from LSDA+DMFT calculations

. We have presented the results of our ab initio calculations carried out by the use of the density functional theory (DFT). We utilized a method which merges the local spin density approximation (LSDA) with the dynamical mean-field theory (DMFT) to account for the electronic correlations using the Hubbard I solver. The LSDA+DMFT calculations were performed for T = 500 K and T = 700 K. The particular emphasis was put on the pressure-induced changes in the electronic band structure related to strongly correlated 4f states. As a reference, we applied the zero

Open access
AB Initio Calculations of CUN@Graphene (0001) Nanostructures for Electrocatalytic Applications

Abstract

Substitution of fossil-based chemical processes by the combination of electrochemical reactions driven by sources of renewable energy and parallel use of H2O and CO2 to produce carbon and hydrogen, respectively, can serve as direct synthesis of bulk chemicals and fuels. We plan to design and develop a prototype of electrochemical reactor combining cathodic CO2-reduction to ethylene and anodic H2O oxidation to hydrogen peroxide. We perform ab initio calculations on the atomistic 2D graphene-based models with attached Cu atoms foreseen for dissociation of CO2 and H2O containing complexes, electronic properties of which are described taking into account elemental electrocatalytical reaction steps. The applicability of the model nanostructures for computer simulation on electrical conductivity of charged Cun/graphene (0001) surface is also reported.

Open access
First-principles investigation of the structural stability and electronic properties of Pd doped monoclinic Cu6Sn5 intermetallic compounds

Abstract

Tri-layer Au/Pd/Ni(P) films have been widely used as surface finish over the Cu pads in high-end packaging applications. It was found that a thin (Cu,Pd)6Sn5 IMC layer was beneficial in effective reducing inter-diffusion between a Cu substrate and a solder, and therefore the growth of the IMC layer and the EM (electromigration) processes. In this study, the structural properties and phase stability of monoclinic Cu6Sn5-based structures with Pd substitutions were studied by using the first-principles method. The (Cu,Pd)6Sn5 structure with the 4e site substituted by Pd has the lowest heat of formation and is the most stable among (Cu,Pd)6Sn5 structures. Hybridization of Pd-d and Sn-p states is a dominant factor for stability improvement. Moreover, Pd atoms concentration corresponding to the most stable structure of (Cu,Pd)6Sn5 was found to be 1.69 %, which is consistent with the experimental results.

Open access
Structural stability, electronic structure and magnetic properties of the new hypothetical half-metallic ferromagnetic full-Heusler alloy CoNiMnSi

Abstract

We investigated the structural stability as well as the mechanical, electronic and magnetic properties of the Full-Heusler alloy CoNiMnSi using the full-potential linearized augmented plane wave (FP-LAPW) method. Two generalized gradient approximations (GGA and GGA + U) were used to treat the exchange-correlation energy functional. The ground state properties of CoNiMnSi including the lattice parameter and bulk modulus were calculated. The elastic constants (Cij) and their related elastic moduli as well as the thermodynamic properties for CoNiMnSi have been calculated for the first time. The existence of half-metallic ferromagnetism (HM-FM) in this material is apparent from its band structure. Our results classify CoNiMnSi as a new HM-FM material with high spin polarization suitable for spintronic applications.

Open access
Diamagnetic cobalt(III)tris(o-ethylxanthate) and nickel(II)bis(o-ethylxanthate)

Abstract

Diamagnetic [Co(xanth)3] and [Ni(xanth)2] complexes have been prepared by reaction of Co(II) and Ni(II) salts with potassium O-ethyl xanthate (Kxanth). The isolated Co(III) and Ni(II) complexes have been characterized by single-crystal X-ray crystallography, UV-VIS and IR spectroscopy, computational methods, and magnetic measurements.

Open access
Ab initio study of GdCo5 magnetic and magneto-optical properties

Abstract

The full potential linearized augmented plane wave method (FLAPW) including the spin-orbit coupling has been used to study the structural, electronic and magnetic properties of GdCo5 compound. The calculations were performed within the local spin density approximation (LSDA) as well as Coulomb corrected LSDA + U approach. The study revealed that the LSDA + U method gave a better representation of the band structure, density of states and magnetic moments than LSDA. It was found that the spin magnetic moment of Co (2c) and Co (3g) atoms in the studied compound is smaller compared to the one in bulk Co. The optical and magneto-optical properties and the magneto-optical Kerr effect have also been investigated.

Open access
Thermal conductivity of silicon doped by phosphorus: ab initio study

Abstract

An original approach to the theoretical calculations of the heat conductivity of crystals based on the first principles molecular dynamics has been proposed. The proposed approach exploits the kinetic theory of phonon heat conductivity and permits calculating several material properties at certain temperature: specific heat, elastic constant, acoustic velocity, mean phonon scattering time and coefficient of thermal conductivity. The method has been applied to silicon and phosphorus doped silicon crystals and the obtained results have been found to be in satisfactory agreement with corresponding experimental data. The proposed computation technique may be applied to the calculations of heat conductivity of pure and doped semiconductors and isolators.

Open access
Raman and infrared spectra, conformations and ab initio calculations of 3-methoxymethylene-2,4-pentanedione

Abstract

The IR (4000-400 cm-1) and Raman (4000-50 cm-1) spectra of 3-methoxymethylene-2,4-pentanedione [H3C-O-CH=C(COCH3)2] as a liquid and solutes in various solvents of different polarity have been recorded at ambient temperature. Additional IR and Raman spectra were obtained for amorphous and crystalline solid state at low temperature. The vibrational spectra revealed that the compound exists at least in two dominant conformers of different polarity and that the conformer present in the solid phase is less polar. NMR spectra in various solvents at different temperatures were also obtained.

The compound can exist in several conformers due to the rotation around O-C= and both =C-C bonds with planar or nonplanar arrangements of heavy atoms. Ab initio MP2 and DFT calculations using a wide scale of basis sets were carried out. According to these calculations six conformational structures of the eight theoretically possible conformational structures with the methoxy group oriented as anti or syn and carbonyl groups oriented as Z or E towards the C=C double bond were obtained at potential energy surface. It has been shown that the conformers with the E orientations of both acetyl groups are not the stable ones. The calculated ab initio MP2 and DFT energies of all found conformers in vacuum suggest the most stable ZEa conformer where Z and E regard to the trans and cis acetyl groups, respectively and a denotes the orientation of the methoxy group. The EZa conformer was calculated as the second most stable one with the energy by at least 10 kJ mol-1 higher. Corrections of the relative energies of single conformers obtained in vacuum on the polar surroundings were done by including the solvent effect into the calculations using IEF Polarizable Continuum Model.

Assignments of the vibrational spectra for the studied compound were made with the aid of normal coordinate calculations employing scaled ab initio force field. The scaled ab initio frequencies as well as calculated energies indicate that ZEa is the conformer present in the solid phase.

Open access
A theoretical study on 2-chloro-5-(2-hydroxyethyl)-4-methoxy-6-methylpyrimidine by DFT/ab initio calculations

Abstract

Quantum chemical calculations have been performed to study the molecular geometry, 1H and 13C NMR chemical shifts, conformational, natural bond orbital (NBO) and nonlinear optical (NLO) properties of the 2-chloro-5-(2-hydroxyethyl)-4- methoxy-6-methylpyrimidine molecule in the ground state using DFT and HF methods with 6-311++G(d,p) basis set. The optimized geometric parameters and 1H and 13C NMR chemical shifts have been compared with the experimental values of the title molecule. The results of the calculations show excellent agreement between the experimental and calculated frequencies at B3LYP/6-311++G(d,p) level. In order to provide a full understanding of the properties of the title molecule in the context of molecular orbital picture, the highest occupied molecular energy level (EHOMO), the lowest unoccupied molecular energy level (ELUMO), the energy difference (DE) between EHOMO and ELUMO, electronegativity (χ), hardness (η) and softness (S) have been calculated using B3LYP/6-311++G(d,p) and HF/6-311++G(d,p) levels. The calculated HOMO and LUMO energies show that the charge transfer occurs within the title molecule.

Open access