75 research outputs found
Hubbard-U calculations for Cu from first-principles Wannier functions
We present first-principles calculations of optimally localized Wannier
functions for Cu and use these for an ab-initio determination of Hubbard
(Coulomb) matrix elements. We use a standard linearized muffin-tin orbital
calculation in the atomic-sphere approximation (LMTO-ASA) to calculate Bloch
functions, and from these determine maximally localized Wannier functions using
a method proposed by Marzari and Vanderbilt. The resulting functions were
highly localized, with greater than 89% of the norm of the function within the
central site for the occupied Wannier states. Two methods for calculating
Coulomb matrix elements from Wannier functions are presented and applied to fcc
Cu. For the unscreened on-site Hubbard for the Cu 3d-bands we have obtained
about 25eV. These results are also compared with results obtained from a
constrained local-density approximation (LDA) calculation.Comment: 13 pages, 8 figures, 5 table
Applicability of the Broken-Bond Rule to the Surface Energy of the fcc Metals
We apply the Green's function based full-potential screened
Korringa-Kohn-Rostoker method in conjunction with the local density
approximation to study the surface energies of the noble and the fcc transition
and metals. The orientation dependence of the transition metal surface
energies can be well described taking into account only the broken bonds
between first neighbors, quite analogous to the behavior we recently found for
the noble metals [see cond-mat/0105207]. The (111) and (100) surfaces of the
metals show a jellium like behavior but for the more open surfaces we find
again the noble metals behavior but with larger deviation from the broken-bond
rule compared to the transition metals. Finally we show that the use of the
full potential is crucial to obtain accurate surface energy anisotropy ratios
for the vicinal surfaces.Comment: 13 pages, 5 figures, to appear in July in Surface Science Vol. 511,1
(2002
Magnetization relaxation in (Ga,Mn)As ferromagnetic semiconductors
We describe a theory of Mn local-moment magnetization relaxation due to p-d
kinetic-exchange coupling with the itinerant-spin subsystem in the
ferromagnetic semiconductor (Ga,Mn)As alloy. The theoretical Gilbert damping
coefficient implied by this mechanism is calculated as a function of Mn moment
density, hole concentration, and quasiparticle lifetime. Comparison with
experimental ferromagnetic resonance data suggests that in annealed strongly
metallic samples, p-d coupling contributes significantly to the damping rate of
the magnetization precession at low temperatures. By combining the theoretical
Gilbert coefficient with the values of the magnetic anisotropy energy, we
estimate that the typical critical current for spin-transfer magnetization
switching in all-semiconductor trilayer devices can be as low as .Comment: 4 pages, 2 figures, submitted to Rapid Communication
Computational materials design for high-T(c) (Ga,Mn)As with Li codoping
Based on first-principles calculations and kinetic Monte Carlo simulations, we design a realistic and practical codoping technique for increasing the concentration of Mn atoms in GaAs and realizing high Curie temperatures in (Ga, Mn) As. We found that using codoping of Li interstitial atoms during the crystal growth has two great advantages. First, due to lower formation energy of Li interstitials compared to Mn interstitials, Li prevents formation of unwanted Mn interstitials. Second, Li interstitials can be removed by using post-growth annealing at low temperatures. This codoping method offers a general strategy to go far beyond the solubility limit and it should be applicable also to other diluted magnetic semiconductor systems
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