892 research outputs found
Curvilinear coordinates for full-core atoms
Curvilinear coordinates, first introduced by F. Gygi for valence-only
electronic systems within the local-density functional theory, can be used to
describe both core and valence electrons in electronic-structure calculations.
A simple and quite general coordinate transformation results in a large, yet
affordable plane-wave energy cutoff for full-core systems (e.g., about 120 Ryd
for carbon or silicon) within the local-density functional theory, and in a
reduced correlation time for full-core variational Monte Carlo calculations.
Numerical tests for isolated Li, C, and Si atoms are presented.Comment: 14 pages, 8 Postscript figures; acknowledgements and two refs. adde
Chemical Hardness, Linear Response, and Pseudopotential Transferability
We propose a systematic method of analyzing pseudopotential transferability
based on linear-response properties of the free atom, including self-consistent
chemical hardness and polarizability. Our calculation of hardness extends the
approach of Teter\cite{teter} not only by including self-consistency, but also
by generalizing to non-diagonal hardness matrices, thereby allowing us to test
for transferability to non-spherically symmetric environments. We apply the
method to study the transferability of norm-conserving pseudopotentials for a
variety of elements in the Periodic Table. We find that the self-consistent
corrections are frequently significant, and should not be neglected. We prove
that the partial-core correction improves the pseudopotential hardness of
alkali metals considerably. We propose a quantity to represent the average
hardness error and calculate this quantity for many representative elements as
a function of pseudopotential cutoff radii. We find that the atomic
polarizabilities are usually well reproduced by the norm-conserving
pseudopotentials. Our results provide useful guidelines for making optimal
choices in the pseudopotential generation procedure.Comment: Revtex (preprint style, 33 pages) + 9 postscript figures A version in
two-column article style with embedded figures is available at
http://electron.rutgers.edu/~dhv/preprints/index.html#l
Pair-distribution functions of the two-dimensional electron gas
Based on its known exact properties and a new set of extensive fixed-node
reptation quantum Monte Carlo simulations (both with and without backflow
correlations, which in this case turn out to yield negligible improvements), we
propose a new analytical representation of (i) the spin-summed
pair-distribution function and (ii) the spin-resolved potential energy of the
ideal two-dimensional interacting electron gas for a wide range of electron
densities and spin polarization, plus (iii) the spin-resolved pair-distribution
function of the unpolarized gas. These formulae provide an accurate reference
for quantities previously not available in analytic form, and may be relevant
to semiconductor heterostructures, metal-insulator transitions and quantum dots
both directly, in terms of phase diagram and spin susceptibility, and
indirectly, as key ingredients for the construction of new two-dimensional spin
density functionals, beyond the local approximation.Comment: 12 pages, 10 figures; misprints correcte
Unified modelling of the thermoelectric properties in SrTiO3
Thermoelectric materials are opening a promising pathway to address energy
conversion issues governed by a competition between thermal and electronic
transport. Improving the efficiency is a difficult task, a challenge that
requires new strategies to unearth optimized compounds. We present a theory of
thermoelectric transport in electron doped SrTiO3, based on a realistic tight
binding model that includes relevant scattering processes. We compare our
calculations against a wide panel of experimental data, both bulk and thin
films. We find a qualitative and quantitative agreement over both a wide range
of temperatures and carrier concentrations, from light to heavily doped.
Moreover, the results appear insensitive to the nature of the dopant La, B, Gd
and Nb. Thus, the quantitative success found in the case of SrTiO3, reveals an
efficient procedure to explore new routes to improve the thermoelectric
properties in oxides.Comment: 5 figures, manuscript submitte
Ab initio Molecular Dynamics in Adaptive Coordinates
We present a new formulation of ab initio molecular dynamics which exploits
the efficiency of plane waves in adaptive curvilinear coordinates, and thus
provides an accurate treatment of first-row elements. The method is used to
perform a molecular dynamics simulation of the CO_2 molecule, and allows to
reproduce detailed features of its vibrational spectrum such as the splitting
of the Raman sigma+_g mode caused by Fermi resonance. This new approach opens
the way to highly accurate ab initio simulations of organic compounds.Comment: 11 pages, 3 PostScript figure
Tailoring strain in SrTiO3 compound by low energy He+ irradiation
The ability to generate a change of the lattice parameter in a near-surface
layer of a controllable thickness by ion implantation of strontium titanate is
reported here using low energy He+ ions. The induced strain follows a
distribution within a typical near-surface layer of 200 nm as obtained from
structural analysis. Due to clamping effect from the underlying layer, only
perpendicular expansion is observed. Maximum distortions up to 5-7% are
obtained with no evidence of amorphisation at fluences of 1E16 He+ ions/cm2 and
ion energies in the range 10-30 keV.Comment: 11 pages, 4 figures, Accepted for publication in Europhysics Letter
(http://iopscience.iop.org/0295-5075
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