In this study, we present results of the electronic density of states (DOS) and bulk magnetic moment of iron (Fe), cobalt (Co) and their alloys (Fe
x
Co
1–
x
;
x
= 1.0, 0.95, …, 0.0). Density ...functional theory with the generalized gradient approximation was applied to obtain geometric and electronic properties. The methodology uses virtual crystal approximation, in conjunction with CASTEP module and the functionals PBE and PBESol of the molecular simulation program Material Studio. We optimized the geometry of the bulk (obtaining their lattice parameters), which the structure was used to determine the bulk magnetic moments. To determine the magnetic moment, we calculated the difference of the electronic DOS of the electrons with spin up and spin down. The geometric optimization and magnetic moment obtained in the present study are very similar to the experimental results, with a maximum error of 8%, which makes the present article interesting.
Ionic conductivity of crosslinked chitosan membranes was studied using techniques of molecular modeling and simulation. The COMPASS force field was used. The simulation allows the description of the ...mechanism of ionic conductivity along the polymer matrix. The theoretical results obtained are compared with experimental results for chitosan membranes. The analysis suggests that the conduction mechanism is portrayed by the overlapping large Polaron tunneling model. In addition, when the chitosan membrane was crosslinked with an appropriate degree of crosslinking its ionic conductivity, at room temperature, was increased by about one order of magnitude. The chitosan membranes can be used as electrolytes in solid state batteries, electric double layer capacitors and fuel cells.
A new approach for computing the atom-in-molecule quantum theory of atoms in molecule (QTAIM) energies in Kohn-Sham density-functional theory is presented and tested by computing QTAIM energies for a ...set of representative molecules. In the new approach, the contribution for the correlation-kinetic energy (T(c)) is computed using the density-functional theory virial relation. Based on our calculations, it is shown that the conventional approach where atomic energies are computed using only the noninteracting part of the kinetic energy might be in error by hundreds of kJ/mol.
In this work we calculate heat capacity of alloy thin films of FeCo on the surface of the plane (110), using three parameters, the concentration x(i), the lattice long range order parameter t(i) and ...the magnetic order parameter σ(i), being i the number of layers of the thin film. The formulations reported by Hill 1 in the context of small particles and Valenta's model 2 can be applied to the film structure when we treat a thin film as a system divided into subsystems equivalent to two-dimensional parallel layers. The FeCo bulk alloy is completely homogeneous while a thin film have spatial discontinuities in their surfaces. We consider three ferromagnetic thin films formed by 11, 15 and 19 layers in the Helmholtz's free energy, which is minimized applying their first partial derivatives with respect to chemical composition, long range order parameter and magnetic order parameter. We calculate internal energy and heat capacity as a function of temperature and we verify that have two jumps as are reported in literature for the bulk; there are many results of bulk or surface effects of FeCo, but no enough results about ferromagnetic FeCo thin films and this fact does this work interesting.
•Heat capacity as a function of temperature for 11, 15 and 19 atomic layers of FeCo thin films are determined.•Curie temperature for Fe0.5Co0.5 thin films with 11, 15 and 19 are obtained.•Bulk and thin films heat capacity of Fe0.5Co0.5 have a similar behavior.•Discontinuity in heat capacity of thin films are similar to to bulk Fe0.5Co0.5.
In recent years, the popularity of metal hydrides has increased considerably for hydrogen storage and their applications in hydrogen fuel cells. Their potential applications for clean energy are ...promissory. However, the temperatures required for adsorption and desorption are extremely high, which range between 500 and 700 K, making their use impractical. To overcome these difficulties, the following work considers using three hydride alloys: magnesium-aluminum (MgAl), magnesium-nickel (MgNi), and magnesium-zinc (MgZn). The Mg concentrations were set to be between 80 and 100 wt% in order to reduce the temperatures of adsorption and desorption in contrast with the temperatures of pure magnesium. The chemisorption and repulsion energies of the hydrogen molecule on the surface (110) of the different metallic alloys were studied at 0, 200, 400, 600, and 700 K, respectively. The study was based on the density functional theory (DFT), with the module DMol
3
of the molecular simulation program Materials Studio, which was used to obtain these energy values. The results confirm that adding aluminum, nickel, or zinc into magnesium matrix increases the chemisorption and decreases the energy repulsion values on surfaces of the metallic alloys, improving the effectiveness of the hydrogen storage.
In this work, we extend our recent study J.I. Rodríguez, J. Autschbach, F.L. Castillo-Alvarado, M.I. Baltazar-Méndez, J. Chem. Phys.
135
, 034109 (2011) to quantify the isomer structure effects on ...the atom-in-cluster polarizabilities of medium size gold clusters Au (
n
= 6, 12, 20, 34, 54). For three isomers for each cluster size, a density functional perturbation theory calculation was performed to compute the cluster polarizability and the polarizability of each atom in the cluster using Bader’s “quantum theory of atoms in molecules” formalism. The cluster polarizability tensor is expressed as a sum of the atom-in-cluster atomic tensors. We found that the strong quadratic correlation (
R
2
= 0.98) in the isotropic polarizability of atoms in the cluster and their distance to the cluster center of mass reported before holds independently of the cluster structure.
One difficult aspect to be overcome within technology of hydrogen and fuel cells is hydrogen storage in solid phase materials. Theoretical studies are indispensable support to guide the ...experimentalist in the development of synthesis or characterization of new materials. DFT (density functional theory) was used to optimize the geometry, and at same time, to obtain final enthalpy of bulk alloys of Mg1−xAlx (0 ≤ x ≤ 0.10) and later it was possible to cleave bulk alloy in the direction of the plane (110) to obtain surface effects. Finally, hydrogen molecules were added at the surface of MgAl in the direction (110) and optimized their geometry in order to obtain their final enthalpies of each one of these alloys. Values of chemisorption energy and repulsion of those alloys were obtained, as well as aluminum optimum concentration for adsorption of hydrogen. The value of binding energy for H2 molecule on magnesium surface is about 0.5 eV.
•The enthalpy of MgAl alloy as a function of composition of aluminum is calculated.•The electronic density of states as a function of composition of aluminum are obtained.•Enthalpies of bulk unit cell and supercell of Mg1−xAlx alloy are decreased when concentration of aluminum are increased.•The binding energy of H2 molecule on the Mg1−xAlx alloy is comparable with experimental results.
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•Theoretical study of cluster complexes Au4-S-CnH2n-S′-Au4′.•The Au-Au and S-S interactions in Au4-S-CnH2n-S′-Au4′ are closed shell.•HOMO-LUMO gap has a zigzag behavior with respect ...to the number of carbon atoms in the complexes Au4-S-CnH2n-S′-Au4′.
We introduce relativistic density functional theory (DFT) calculations on the gold cluster complexes (cluster-molecule-cluster) Au4-S-CnH2n-S′-Au4′ (n=2–5). The structural, electronic and relativistic (ZORA) Bader's quantum theory of atoms in molecules (QTAIM) properties of the two lowest-energy complex isomers were computed as a function of the alkanedithiol size (n). The lowest-energy isomer is a triplet spin state independently of the complex size. According to QTAIM, the Au-Au and S-Au bonds are classified as closed shell (non-covalent) type. The HOMO-LUMO gap of the cluster complexes shows a zigzag behavior typical of gold nanoclusters with respect to the size of the alkanedithiol chain (n).
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