2,076 research outputs found
Extending Hirshfeld-I to bulk and periodic materials
In this work, a method is described to extend the iterative Hirshfeld-I
method, generally used for molecules, to periodic systems. The implementation
makes use of precalculated pseudo-potential based charge density distributions,
and it is shown that high quality results are obtained for both molecules and
solids, such as ceria, diamond, and graphite. The use of such grids makes the
implementation independent of the solid state or quantum chemical code used for
studying the system. The extension described here allows for easy calculation
of atomic charges and charge transfer in periodic and bulk systems.Comment: 11 pages, 4 Tables, 5 Figures, pre-referee draft only, much extended
post referee version only available at publishe
Reply to 'Comment on "Extending Hirshfeld-I to bulk and periodic materials" '
The issues raised in the comment by T.A. Manz are addressed through the
presentation of calculated atomic charges for NaF, NaCl, MgO, SrTiO and
LaCeO, using our previously presented method for calculating
Hirshfeld-I charges in Solids [J. Comput. Chem.. doi: 10.1002/jcc.23088]. It is
shown that the use of pseudo-valence charges is sufficient to retrieve the full
all-electron Hirshfeld-I charges to good accuracy. Furthermore, we present
timing results of different systems, containing up to over atoms,
underlining the relatively low cost for large systems. A number of theoretical
issues is formulated, pointing out mainly that care must be taken when deriving
new atoms in molecules methods based on "expectations" for atomic charges.Comment: 7 pages, 2 Tables, 2 figure
Continuous-feed nanocasting process for the synthesis of bismuth nanowire composites
We present a novel, continuous-feed nanocasting procedure for the synthesis
of bismuth nanowire structures embedded in the pores of a mesoporous silica
template. The immobilization of a bismuth salt inside the silica template from
a diluted metal salt solution yields a sufficiently high loading to obtain
electrically conducting bulk nanowire composite samples after reduction and
sintering the nanocomposite powders. Electrical resistivity measurements of
sintered bismuth nanowires embedded in the silica template reveal
size-quantization effects
Z-Pencils
The matrix pencil (A,B) = {tB-A | t \in C} is considered under the
assumptions that A is entrywise nonnegative and B-A is a nonsingular M-matrix.
As t varies in [0,1], the Z-matrices tB-A are partitioned into the sets L_s
introduced by Fiedler and Markham. As no combinatorial structure of B is
assumed here, this partition generalizes some of their work where B=I. Based on
the union of the directed graphs of A and B, the combinatorial structure of
nonnegative eigenvectors associated with the largest eigenvalue of (A,B) in
[0,1) is considered.Comment: 8 pages, LaTe
Tuning of CeO buffer layers for coated superconductors through doping
The appearance of microcracks in CeO buffer layers, as used in buffer
layer architectures for coated superconductors, indicates the presence of
stress between this buffer layer and the substrate. This stress can originate
from the differences in thermal expansion or differences in lattice parameters
between the CeO buffer layer and the substrate. In this article, we study,
by means of \textit{ab initio} density functional theory calculations, the
influence of group IV doping elements on the lattice parameter and bulk modulus
of CeO. Vegard's law behavior is found for the lattice parameter in systems
without oxygen vacancies, and the Shannon crystal radii for the doping elements
are retrieved from the lattice expansions. We show that the lattice parameter
of the doped CeO can be matched to that of the LaZrO coated NiW
substrate substrate for dopant concentrations of about , and that bulk
modulus matching is either not possible or would require extreme doping
concentrations.Comment: 5 pages, 1 table, 2 figures, EMRS 2011 Fall meeting symposium on
Stress, structure and stoichiometry effects on nanomaterial
Eigenvalues of matrices with tree graphs
AbstractWhen the undirected graph of a real square matrix is a tree of forest, we establish finitely computable tests yielding information about the magnitudes and multiplicities to the eigenvalues of the matrix. Applying these tests to system designs expressed as signed directed graphs can be sufficient to guarantee controllability of the associated linear dynamical systems
Some remarks on matrix stability with application to Turing instability
AbstractAn example of a 4×4 matrix is given that provides a counterexample to a result on Turing (diffusion-driven) instability and also answers negatively a conjecture on strong stability. Such instability is shown to arise from nonreal eigenvalues. The relevance and the connection of our example to classes of matrix stability known in the literature are discussed
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