28,310 research outputs found
Magnetic monolayer LiN: Density Functional Theory Calculations
Density functional theory (DFT) calculations are used to investigate the
electronic and magnetic structures of a two-dimensional (2D) monolayer
LiN. It is shown that bulk LiN is a non-magnetic semiconductor. The
non-spinpolarized DFT calculations show that electrons of N in 2D LiN
form a narrow band at the Fermi energy due to a low coordination
number, and the density of states at the Fermi energy ()) is
increased as compared with bulk LiN. The large ) shows
instability towards magnetism in Stoner's mean field model. The spin-polarized
calculations reveal that 2D LiN is magnetic without intrinsic or impurity
defects. The magnetic moment of 1.0\, in 2D LiN is mainly
contributed by the electrons of N, and the band structure shows
half-metallic behavior. {Dynamic instability in planar LiN monolayer is
observed, but a buckled LiN monolayer is found to be dynamically stable.}
The ferromagnetic (FM) and antiferromagnetic (AFM) coupling between the N atoms
is also investigated to access the exchange field strength. {We found that
planar (buckled) 2D LiN is a ferromagnetic material with Curie
temperature of 161 (572) K.}Comment: Euro Phys. Lett. 2017 (Accepted
Artificial molecular quantum rings: Spin density functional theory calculations
The ground states of artificial molecules made of two vertically coupled
quantum rings are studied within the spin density functional theory for systems
containing up to 13 electrons. Quantum tunneling effects on the electronic
structure of the coupled rings are analyzed. For small ring radius, our results
recover those of coupled quantum dots. For intermediate and large ring radius,
new phases are found showing the formation of new diatomic artificial ring
molecules. Our results also show that the tunneling induced phase transitions
in the coupled rings occur at much smaller tunneling energy as compared to
those for coupled quantum dot systems.Comment: 10 pages, 6 figure
Benchmark density functional theory calculations for nano-scale conductance
We present a set of benchmark calculations for the Kohn-Sham elastic
transmission function of five representative single-molecule junctions. The
transmission functions are calculated using two different density functional
theory (DFT) methods, namely an ultrasoft pseudopotential plane wave code in
combination with maximally localized Wannier functions, and the norm-conserving
pseudopotential code Siesta which applies an atomic orbital basis set. For all
systems we find that the Siesta transmission functions converge toward the
plane-wave result as the Siesta basis is enlarged. Overall, we find that an
atomic basis with double-zeta and polarization is sufficient (and in some cases
even necessary) to ensure quantitative agreement with the plane-wave
calculation. We observe a systematic down shift of the Siesta transmission
functions relative to the plane-wave results. The effect diminishes as the
atomic orbital basis is enlarged, however, the convergence can be rather slow.Comment: 10 pages, 7 figure
Density functional theory calculations of adsorption-induced surface stress changes
Density functional theory calculations of adsorbate-induced surface stress changes have been performed for a number of adsorbate and overlayer systems for which experimental data exists, namely: oxygen and sulphur adsorption on Ni(1 0 0); oxygen adsorption on W(1 1 0); pseudomorphic growth of Ni on Cu(1 0 0) and of Fe on W(1 1 0); oxygen adsorption on a 5 ML pseudomorphic film of Ni(1 0 0) grown on Cu(1 0 0). The theoretical calculations reproduce all the qualitative features of the experimental data, but there are some significant quantitative differences, most notably for the two atomic adsorbates on the bulk Ni(1 0 0) surface, for which the theoretical stress changes are substantially smaller than the experimental ones, a situation not obviously attributable to experimental error. For the W(1 1 0)/Fe system there is also a marked difference between experiment and theory in the coverage at which key surface stress changes occur
Density functional theory calculations on magnetic properties of actinide compounds
We have performed a detailed analysis of the magnetic (collinear and
noncollinear) order and atomic and the electron structures of UO2, PuO2 and UN
on the basis of density functional theory with the Hubbard electron correlation
correction (DFT+U). We have shown that the 3-k magnetic structure of UO2 is the
lowest in energy for the Hubbard parameter value of U=4.6 eV (and J=0.5 eV)
consistent with experiments when Dudarev's formalism is used. In contrast to
UO2, UN and PuO2 show no trend for a distortion towards rhombohedral structure
and, thus, no complex 3-k magnetic structure is to be anticipated in these
materials.Comment: 5 pages, 3 figures 1 table, submitted to Phys. Chem. Chem. Phy
Fragment Approach to Constrained Density Functional Theory Calculations using Daubechies Wavelets
In a recent paper we presented a linear scaling Kohn-Sham density functional
theory (DFT) code based on Daubechies wavelets, where a minimal set of
localized support functions is optimized in situ and therefore adapted to the
chemical properties of the molecular system. Thanks to the systematically
controllable accuracy of the underlying basis set, this approach is able to
provide an optimal contracted basis for a given system: accuracies for ground
state energies and atomic forces are of the same quality as an uncontracted,
cubic scaling approach. This basis set offers, by construction, a natural
subset where the density matrix of the system can be projected. In this paper
we demonstrate the flexibility of this minimal basis formalism in providing a
basis set that can be reused as-is, i.e. without reoptimization, for
charge-constrained DFT calculations within a fragment approach. Support
functions, represented in the underlying wavelet grid, of the template
fragments are roto-translated with high numerical precision to the required
positions and used as projectors for the charge weight function. We demonstrate
the interest of this approach to express highly precise and efficient
calculations for preparing diabatic states and for the computational setup of
systems in complex environments
Density functional theory calculations of anisotropic constitutive relationships in alpha-cyclotrimethylenetrinitramine
Constitutive relationships in the crystalline energetic material alpha-cyclotrimethylenetrinitramine (alpha-RDX) have been investigated using first-principles density functional theory. The equilibrium properties of alpha-RDX including unit cell parameters and bulk modulus, as well as the hydrostatic equation of state (EOS), have been obtained and compared with available experimental data. The isotropic EOS has been extended to include the anisotropic response of alpha-RDX by performing uniaxial compressions normal to several low-index planes, {100}, {010}, {001}, {110}, {101}, {011}, and {111}, in the Pbca space group. The uniaxial-compression data exhibit a considerable anisotropy in the principal stresses, changes in energy, band gaps, and shear stresses, which might play a role in the anisotropic behavior of alpha-RDX under shock loading
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