7,693 research outputs found
Forces and atomic relaxations in the pSIC approach with ultrasoft pseudopotentials
We present the scheme that allows for efficient calculations of forces in the
framework of pseudopotential self-interaction corrected (pSIC) formulation of
the density functional theory. The scheme works with norm conserving and also
with ultrasoft pseudopotentials and has been implemented in the plane-wave
basis code {\sc quantum espresso}. We have performed tests of the internal
consistency of the derived expressions for forces considering ZnO and CeO
crystals. Further, we have performed calculations of equilibrium geometry for
LaTiO, YTiO, and LaMnO perovskites and also for Re and Mn pairs in
silicon. Comparison with standard DFT and DFT+U approaches shows that in the
cases where spurious self-interaction matters, the pSIC approach predicts
different geometry, very often closer to the experimental data.Comment: 11 pages, 2 figure
Influence of band structure effects on domain-wall resistance in diluted ferromagnetic semiconductors
Intrinsic domain-wall resistance (DWR) in (Ga,Mn)As is studied theoretically
and compared to experimental results. The recently developed model of spin
transport in diluted ferromagnetic semiconductors [Van Dorpe et al., Phys. Rev.
B 72, 205322 (2005)] is employed. The model combines the disorder-free
Landauer-B\"uttiker formalism with the tight-binding description of the host
band structure. The obtained results show how much the spherical 4x4 kp model
[Nguyen, Shchelushkin, and Brataas, cond-mat/0601436] overestimates DWR in the
adiabatic limit, and reveal the dependence of DWR on the magnetization profile
and crystallographic orientation of the wall.Comment: 4 pages, 4 figures, submitted to Phys. Rev. B - Rapid Com
Measurement of the Scintillation Efficiency of Na Recoils in NaI(Tl) down to 10 keV Nuclear Recoil Energy relevant to Dark Matter Searches
We present preliminary results of measurements of the quenching factor for Na
recoils in NaI(Tl) at room temperature, made at a dedicated neutron facility at
the University of Sheffield. Measurements have been performed with a 2.45 MeV
mono-energetic neutron generator in the energy range from 10 keV to 100 keV
nuclear recoil energy. A BC501A liquid scintillator detector was used to tag
neutrons. Cuts on pulse-shape discrimination from the BC501A liquid
scintillator detector and neutron time-of-flight were performed on pulses
recorded by a digitizer with a 2 ns sampling time. Measured quenching factors
range from 19% to 26%, in agreement with other experiments. From pulse-shape
analysis, a mean time of pulses from electron and nuclear recoils are compared
down to 2 keV electron equivalent energy.Comment: to appear in Proc. 6th Int. Workshop on the Identification of Dark
Matter, 11-16 September 2006, Rhodes, Greece; 6 pages, 4 figures; corrected
preliminary theoretical estimation curve plotted in figure
Origin of bulk uniaxial anisotropy in zinc-blende dilute magnetic semiconductors
It is demonstrated that the nearest neighbor Mn pair on the GaAs (001)
surface has a lower energy for the [-110] direction comparing to the [110]
case. According to the group theory and the Luttinger's method of invariants,
this specific Mn distribution results in bulk uniaxial in-plane and
out-of-plane anisotropies. The sign and magnitude of the corresponding
anisotropy energies determined by a perturbation method and ab initio
computations are consistent with experimental results.Comment: 5 pages, 1 figur
Beyond homozygosity mapping: family-control analysis based on Hamming distance for prioritizing variants in exome sequencing
A major challenge in current exome sequencing in autosomal recessive (AR) families is the lack of an effective method to prioritize single-nucleotide variants (SNVs). AR families are generally too small for linkage analysis, and length of homozygous regions is unreliable for identification of causative variants. Various common filtering steps usually result in a list of candidate variants that cannot be narrowed down further or ranked. To prioritize shortlisted SNVs we consider each homozygous candidate variant together with a set of SNVs flanking it. We compare the resulting array of genotypes between an affected family member and a number of control individuals and argue that, in a family, differences between family member and controls should be larger for a pathogenic variant and SNVs flanking it than for a random variant. We assess differences between arrays in two individuals by the Hamming distance and develop a suitable test statistic, which is expected to be large for a causative variant and flanking SNVs. We prioritize candidate variants based on this statistic and applied our approach to six patients with known pathogenic variants and found these to be in the top 2 to 10 percentiles of ranks
On non-completely positive quantum dynamical maps on spin chains
The new arguments based on Majorana fermions indicating that non-completely
positive maps can describe open quantum evolution are presented.Comment: published; small change
Spin-torque efficiency enhanced by Rashba spin splitting in three dimensions
We examine a spin torque induced by the Rashba spin-orbit coupling in three
dimensions within the Boltzmann transport theory. We analytically calculate the
spin torque and show how its behavior is related with the spin topology in the
Fermi surfaces by studying the Fermi-energy dependence of the spin torque.
Moreover we discuss the spin-torque efficiency which is the spin torque divided
by the applied electric current in association with the current-induced
magnetization reversal. It is found that high spin-torque efficiency is
achieved when the Fermi energy lies on only the lower band and there exists an
optimal value for the Rashba parameter, where the spin-torque efficiency
becomes maximum.Comment: 7 pages, 5 figure
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