2,294 research outputs found
Predicting polarization enhancement in multicomponent ferroelectric superlattices
Ab initio calculations are utilized as an input to develop a simple model of
polarization in epitaxial short-period CaTiO3/SrTiO3/BaTiO3 superlattices grown
on a SrTiO3 substrate. The model is then combined with a genetic algorithm
technique to optimize the arrangement of individual CaTiO3, SrTiO3 and BaTiO3
layers in a superlattice, predicting structures with the highest possible
polarization and a low in-plane lattice constant mismatch with the substrate.
This modelling procedure can be applied to a wide range of layered
perovskite-oxide nanostructures providing guidance for experimental development
of nanoelectromechanical devices with substantially improved polar properties.Comment: 4 pages, submitted to PR
Comment on "Weyl fermions and the anomalous Hall effect in metallic ferromagnets"
We point out that, contrary to an assertion by Chen, Bergman and Burkov
[Phys. Rev. B 88, 125110 (2013)], the non-quantized part of the intrinsic
anomalous Hall conductivity can indeed be expressed as a Fermi-surface property
even when Weyl points are present in the bandstructure.Comment: Submitted to Physical Review
First-principles study of epitaxial strain in perovskites
Using an extension of a first-principles method developed by King-Smith and
Vanderbilt [Phys. Rev. B {\bf 49}, 5828 (1994)], we investigate the effects of
in-plane epitaxial strain on the ground-state structure and polarization of
eight perovskite oxides: BaTiO, SrTiO, CaTiO, KNbO, NaNbO,
PbTiO, PbZrO, and BaZrO. In addition, we investigate the effects of
a nonzero normal stress. The results are shown to be useful in predicting the
structure and polarization of perovskite oxide thin films and superlattices.Comment: 10 page
Compositional Inversion Symmetry Breaking in Ferroelectric Perovskites
Ternary cubic perovskite compounds of the form A_(1/3)A'_(1/3)A''_(1/3)BO_3
and AB_(1/3)B'_(1/3)B''_(1/3)O_3, in which the differentiated cations form an
alternating series of monolayers, are studied using first-principles methods.
Such compounds are representative of a possible new class of materials in which
ferroelectricity is perturbed by compositional breaking of inversion symmetry.
For isovalent substitution on either sublattice, the ferroelectric double-well
potential is found to persist, but becomes sufficiently asymmetric that
minority domains may no longer survive. The strength of the symmetry breaking
is enormously stronger for heterovalent substitution, so that the double-well
behavior is completely destroyed. Possible means of tuning between these
behaviors may allow for the optimization of resulting materials properties.Comment: 4 pages, two-column style with 3 postscript figures embedded. Uses
REVTEX and epsf macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/index.html#sai_is
Elastic analysis of shear test plate
March, 1970.CER70-71RHJ-MDV19.Includes bibliographical references
Behavior of shear test structure
June, 1970.CER70-71RCS-MDV20.Includes bibliographical references
First-principles theory of ferroelectric phase transitions for perovskites: The case of BaTiO3
We carry out a completely first-principles study of the ferroelectric phase
transitions in BaTiO. Our approach takes advantage of two features of these
transitions: the structural changes are small, and only low-energy distortions
are important. Based on these observations, we make systematically improvable
approximations which enable the parameterization of the complicated energy
surface. The parameters are determined from first-principles total-energy
calculations using ultra-soft pseudopotentials and a preconditioned
conjugate-gradient scheme. The resulting effective Hamiltonian is then solved
by Monte Carlo simulation. The calculated phase sequence, transition
temperatures, latent heats, and spontaneous polarizations are all in good
agreement with experiment. We find the transitions to be intermediate between
order-disorder and displacive character. We find all three phase transitions to
be of first order. The roles of different interactions are discussed.Comment: 33 pages latex file, 9 figure
Photoelasticity of sodium silicate glass from first principles
Based on density-functional perturbation theory we have computed the
photoelastic tensor of a model of sodium silicate glass of composition
(NaO)(SiO) (NS3). The model (containig 84 atoms) is
obtained by quenching from the melt in combined classical and Car-Parrinello
molecular dynamics simulations. The calculated photoelastic coefficients are in
good agreement with experimental data. In particular, the calculation
reproduces quantitatively the decrease of the photoelastic response induced by
the insertion of Na, as measured experimentally.
The extension to NS3 of a phenomenological model developed in a previous work
for pure a-SiO indicates that the modulation upon strain of other
structural parameters besides the SiOSi angles must be invoked to explain the
change in the photoelstic response induced by Na
Electronic structure interpolation via atomic orbitals
We present an efficient scheme for accurate electronic structure
interpolations based on the systematically improvable optimized atomic
orbitals. The atomic orbitals are generated by minimizing the spillage value
between the atomic basis calculations and the converged plane wave basis
calculations on some coarse -point grid. They are then used to calculate the
band structure of the full Brillouin zone using the linear combination of
atomic orbitals (LCAO) algorithms. We find that usually 16 -- 25 orbitals per
atom can give an accuracy of about 10 meV compared to the full {\it ab initio}
calculations. The current scheme has several advantages over the existing
interpolation schemes. The scheme is easy to implement and robust which works
equally well for metallic systems and systems with complex band structures.
Furthermore, the atomic orbitals have much better transferability than the
Shirley's basis and Wannier functions, which is very useful for the
perturbation calculations
Accurate calculation of polarization-related quantities in semiconductors
We demonstrate that polarization-related quantities in semiconductors can be
predicted accurately from first-principles calculations using the appropriate
approach to the problem, the Berry-phase polarization theory. For III-V
nitrides, our test case, we find polarizations, polarization differences
between nitride pairs, and piezoelectric constants quite close to their
previously established values. Refined data are nevertheless provided for all
the relevant quantities.Comment: RevTeX 4 pages, no figure
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