3,085 research outputs found
Adsorption of H2O, NH3, CO, NO2, and NO on graphene: A first-principles study
Motivated by the recent realization of graphene sensors to detect individual
gas molecules, we investigate the adsorption of H2O, NH3, CO, NO2, and NO on a
graphene substrate using first-principles calculations. The optimal adsorption
position and orientation of these molecules on the graphene surface is
determined and the adsorption energies are calculated. Molecular doping, i.e.
charge transfer between the molecules and the graphene surface, is discussed in
light of the density of states and the molecular orbitals of the adsorbates.
The efficiency of doping of the different molecules is determined and the
influence of their magnetic moment is discussed.Comment: 6 pages, 6 figure
First principles investigation of the electronic structure of La2MnNiO6: A room-temperature insulating ferromagnet
Using first principles calculations within DFT based on the full potential
APW+lo method, we calculated the electronic and magnetic structures for the
ferromagnetic and antiferromagnetic states of La2MnNiO6 and analyzed the site
projected density of states and electronic band structures. Our calculations
show that the ground state of La2MnNiO6 is ferromagnetic insulating with the
magnetization in agreement with Hund's first rule and experimental findings.Comment: 10 pages, 3 figure
The mystery of relationship of mechanics and field in the many-body quantum world
We have revealed three fatal errors incurred from a blind transferring of
quantum field methods into the quantum mechanics. This had tragic consequences
because it produced crippled model Hamiltonians, unfortunately considered
sufficient for a description of solids including superconductors. From there,
of course, Fr\"ohlich derived wrong effective Hamiltonian, from which incorrect
BCS theory arose.
1) Mechanical and field patterns cannot be mixed. Instead of field methods
applied to the mechanical Born-Oppenheimer approximation we have entirely to
avoid it and construct an independent and standalone field pattern. This leads
to a new form of the Bohr's complementarity on the level of composite systems.
2) We have correctly to deal with the center of gravity, which is under the
field pattern "materialized" in the form of new quasipartiles - rotons and
translons. This leads to a new type of relativity of internal and external
degrees of freedom and one-particle way of bypassing degeneracies (gap
formation).
3) The possible symmetry cannot be apriori loaded but has to be aposteriori
obtained as a solution of field equations, formulated in a general form without
translational or any other symmetry. This leads to an utterly revised view of
symmetry breaking in non-adiabatic systems, namely Jahn-Teller effect and
superconductivity. These two phenomena are synonyms and share a unique symmetry
breaking.Comment: 24 pages, 9 sections; remake of abstract, introduction and
conclusion; more physics, less philosoph
Robust ab initio calculation of condensed matter: transparent convergence through semicardinal multiresolution analysis
We present the first wavelet-based all-electron density-functional
calculations to include gradient corrections and the first in a solid. Direct
comparison shows this approach to be unique in providing systematic
``transparent'' convergence, convergence with a priori prediction of errors, to
beyond chemical (millihartree) accuracy. The method is ideal for exploration of
materials under novel conditions where there is little experience with how
traditional methods perform and for the development and use of chemically
accurate density functionals, which demand reliable access to such precision.Comment: 4 pages, 3 figures, 4 tables. Submitted to Phys. Rev. Lett. (updated
to include GGA
Ab initio phonon dispersion curves and interatomic force constants of barium titanate
The phonon dispersion curves of cubic BaTiO_3 have been computed within a
first-principles approach and the results compared to the experimental data.
The curves obtained are very similar to those reported for KNbO_3 by Yu and
Krakauer [Phys. Rev. Lett. 74, 4067 (1995)]. They reveal that correlated atomic
displacements along chains are at the origin of the ferroelectric
instability. A simplified model illustrates that spontaneous collective
displacements will occur when a dozen of aligned atoms are coupled. The
longitudinal interatomic force constant between nearest neighbour Ti and O
atoms is relatively weak in comparison to that between Ti atoms in adjacent
cells. The small coupling between Ti and O displacements seems however
necessary to reproduce a ferroelectric instability.Comment: 12 pages, 4 figure
Variational finite-difference representation of the kinetic energy operator
A potential disadvantage of real-space-grid electronic structure methods is
the lack of a variational principle and the concomitant increase of total
energy with grid refinement. We show that the origin of this feature is the
systematic underestimation of the kinetic energy by the finite difference
representation of the Laplacian operator. We present an alternative
representation that provides a rigorous upper bound estimate of the true
kinetic energy and we illustrate its properties with a harmonic oscillator
potential. For a more realistic application, we study the convergence of the
total energy of bulk silicon using a real-space-grid density-functional code
and employing both the conventional and the alternative representations of the
kinetic energy operator.Comment: 3 pages, 3 figures, 1 table. To appear in Phys. Rev. B. Contribution
for the 10th anniversary of the eprint serve
Strain-Dependence of Surface Diffusion: Ag on Ag(111) and Pt(111)
Using density-functional theory with the local-density approximation and the
generalized gradient approximation we compute the energy barriers for surface
diffusion for Ag on Pt(111), Ag on one monolayer of Ag on Pt(111), and Ag on
Ag(111). The diffusion barrier for Ag on Ag(111) is found to increase linearly
with increasing lattice constant. We also discuss the reconstruction that has
been found experimentally when two Ag layers are deposited on Pt(111). Our
calculations explain why this strain driven reconstruction occurs only after
two Ag layers have been deposited.Comment: 4 pages, 3 figures, Phys. Rev. B 55 (1997), in pres
Theoretical and computational study of high pressure structures in barium
Recent high pressure work has suggested that elemental barium forms a high
pressure self-hosting structure (Ba IV) involving two `types' of barium atom.
Uniquely among reported elemental structures it cannot be described by a single
crystalline lattice, instead involving two interpenetrating incommensurate
lattices. In this letter we report pseudopotential calculations demonstrating
the stability and the potentially disordered nature of the `guest' structure.
Using band structures and nearly-free electron theory we relate the appearance
of Ba IV to an instability in the close-packed structure, demonstrate that it
has a zero energy vibrational mode, and speculate about the structure's
stability in other divalent elements.Comment: 4 pages and 5 figures. To appear in PR
Coupled cluster calculations of ground and excited states of nuclei
The standard and renormalized coupled cluster methods with singles, doubles,
and noniterative triples and their generalizations to excited states, based on
the equation of motion coupled cluster approach, are applied to the He-4 and
O-16 nuclei. A comparison of coupled cluster results with the results of the
exact diagonalization of the Hamiltonian in the same model space shows that the
quantum chemistry inspired coupled cluster approximations provide an excellent
description of ground and excited states of nuclei. The bulk of the correlation
effects is obtained at the coupled cluster singles and doubles level. Triples,
treated noniteratively, provide the virtually exact description
Soliton effects in dangling-bond wires on Si(001)
Dangling bond wires on Si(001) are prototypical one dimensional wires, which
are expected to show polaronic and solitonic effects. We present electronic
structure calculations, using the tight binding model, of solitons in
dangling-bond wires, and demonstrate that these defects are stable in
even-length wires, although approximately 0.1 eV higher in energy than a
perfect wire. We also note that in contrast to conjugated polymer systems,
there are two types of soliton and that the type of soliton has strong effects
on the energetics of the bandgap edges, with formation of intra-gap states
between 0.1 eV and 0.2 eV from the band edges. These intra-gap states are
localised on the atoms comprising the soliton.Comment: 6 pages, 3 figures, 3 tables, submitted to Phys. Rev.
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