47 research outputs found
Formulation of the augmented plane-wave and muffin-tin orbital method
A mixed basis all-electron full-potential method, which uses two kinds of
augmented waves, the augmented plane waves and the muffin-tin orbitals
simultaneously, in addition to the local orbitals, was proposed by Kotani and
van Schilfgaarde in Phys. Rev. B81, 125117(2010). We named it the PMT method.
In this paper, this mixed basis method is reformulated on the basis of a new
formalism named as the 3-component formalism, which is a mathematically
transparent version of the additive augmentation originally due to Soler and
Williams in Phys. Rev. B47, 6784(1993). Atomic forces are easily derived
systematically. We discuss some problems in the mixed basis method and ways to
manage them. In addition, we compare the method with the PAW method on the same
footing. This PMT method is the basis for our new development of the
quasiparticle self-consistent method in J.Phys.Soc.Jpn 83, 094711(2014)
Quasiparticle self-consistent GW study of LaNiO and LaNiO/LaAlO superlattice
Using quasiparticle self-consistent calculations we examined the
electronic structure of LaNiO and the LaNiO/LaAlO superlattice. The
effects of electron correlation in Ni- bands were reasonably well described
without any {\it ad hoc} parameter and without the ambiguity related to the
double-counting and downfolding issues. The effective mass is about
enhanced compared to the GGA result. One band feature, which is believed to be
essential for the cuprate-like superconductivity, is not realized and the
central Fermi surface pocket does not disappear. Our result is consistent with
a recent dynamical mean field calculation based on the -- model and in
contrast to the result from a -band only model
Accurate energy bands calculated by the hybrid quasiparticle self-consistent GW method implemented in the ecalj package
We have recently implemented a new version of the quasiparticle
self-consistent GW (QSGW) method in the ecalj package released at
http://github.com/tkotani/ecalj. Since the new version of the ecalj is
numerically stable and accurate compared to the previous versions, we can
perform calculations easily without being bothered with setting input
parameters. Here we examine its ability to describe energy band properties,
e.g., band-gap energy, eigenvalues at special points and effective mass, for
variety of semiconductors and insulators. We treat C, Si, Ge, Sn, SiC (in 2H,
3C, and 4H structures), (Al, Ga, N)x(N, P, As, Pb), (Zn, Cd, Mg)x(O, S, Se,
Te), SiO2, HfO2, ZrO2, SrTiO3, PbS, PbTe, MnO, NiO, and HgO. We propose that a
hybrid QSGW method, where we mix 80 percent of QSGW and 20 percent of LDA,
gives universally good agreement with experiments for these materials.Comment: 8 pages, 3 figures, 4 table
Nitrogen as the best interstitial dopant among =B, C, N, O and F for strong permanent magnet NdFeTi: First-principles study
We study magnetic properties of NdFeTi, where =B, C, N, O, and
F, by using the first-principles calculation based on the density functional
theory. Its parent compound NdFeTi has the ThMn structure, which
has the symmetry of space group , No. 139. The magnetization increases
by doping B, C, N, O, and F at the site of the ThMn structure. The
amount of the increase is larger for =N, O, F than for =B, C. On the
other hand, the crystal field parameter ,
which controls the axial magnetic anisotropy of the Nd magnetic moment,
depends differently on the dopant. With increase of the atomic number from
=B, increases, takes a maximum value for
=N, and then turns to decrease. This suggests that in NdFeTi,
nitrogen is the most appropriate dopant among B, C, N, O, and F for permanent
magnets in terms of magnetization and anisotropy. The above calculated
properties are explained based on the detailed analysis of the electronic
structures of NdFeTi.Comment: 14 pages, 19 figure
Theoretical study of electronic and atomic structures of (MnO)n
We calculate the electronic and atomic structure of (MnO)n (n=1-4) using the
HF exchange, VWN, PBE and B3LYP exchange-correlation functionals. We also
perform diffusion Monte Carlo calculation to evaluate more accurate energies.
We ompare these results and discuss the accuracy of the exchange-correlation
functionals.Comment: 11 page
Quasiparticle self-consistent GW calculation of SrRuO and SrRuO:
Using quasiparticle self-consistent calculations, we re-examined the
electronic structure of SrRuO and SrRuO. Our calculations show that
the correlation effects beyond the conventional LDA (local density
approximation) and GGA (generalized gradient approximation) are reasonably well
captured by QS self-energy without any {\it ad hoc} parameter or any
ambiguity related to the double-counting and the downfolding issues. While the
spectral weight transfer to the lower and upper Hubbard band is not observed,
the noticeable bandwidth reduction and effective mass enhancement are obtained.
Important features in the electronic structures that have been debated over the
last decades such as the photoemission spectra at around eV in
SrRuO and the half-metallicity for SrRuO are discussed in the light
of our QS results and in comparison with the previous studies. The
promising aspects of QS are highlighted as the first-principles calculation
method to describe the moderately correlated 4 transition metal oxides along
with its limitations.Comment: Phys. Rev. B (in press
Effect of -site substitution and the pressure on stability of Fe: A first-principles study
We theoretically study the structural stability of Fe with the
ThMn structure (: rare-earth elements, La, Pr, Nd, Sm, Gd, Dy, Ho,
Er, Tm, Lu, Y, or Sc, or group-IV elements, Zr or Hf) based on density
functional theory. The formation energy has a strong correlation with the
atomic radius of . The formation energy relative to simple substances
decreases as the atomic radius decreases, except for Sc and Hf, while that
relative to Fe and bcc Fe has a minimum for Dy. The present
results are consistent with recent experimental reports in which the partial
substitution of Zr at sites stabilizes Fe-type compounds with
Nd or Sm. Our results also suggest that the partial substitution of Y, Dy,
Ho, Er, or Tm for Nd or Sm is a possible way to enhance the stability of the
ThMn structure. Under hydrostatic pressure, the formation enthalpy
decreases up to 6 GPa and then starts to increase at higher
pressures.Comment: 6 pages, 6 figure
Model-mapped RPA for determining the effective Coulomb interaction
We present a new method to obtain interaction part of a model Hamiltonian
from the result of the first-principles calculation. The effective interaction
contained in the model is determined based on the random phase approximation
(RPA). In contrast to previous methods such as projected RPA or constrained
RPA, the new method takes into account the long-range part of the polarization
effect when determining the interaction in the model. After we discuss problems
in previous RPA methods, we will give the formulation of the new method, and
show how it works for the single-band Hubbard model of HgBaCuO.Comment: 6 page
Direct theoretical evidence for weaker correlations in electron-doped and Hg-based hole-doped cuprates
Many important questions for high- cuprates are closely related to the
insulating nature of parent compounds. While there has been intensive
discussion on this issue, all arguments rely strongly on, or are closely
related to, the correlation strength of the materials. Clear understanding has
been seriously hampered by the absence of a direct measure of this interaction,
traditionally denoted by . Here, we report a first-principles estimation of
for several different types of cuprates. The values clearly increase as
a function of the inverse bond distance between apical oxygen and copper. Our
results show that the electron-doped cuprates are less correlated than their
hole-doped counterparts, which supports the Slater picture rather than the Mott
picture. Further, the values significantly vary even among the hole-doped
families. The correlation strengths of the Hg-cuprates are noticeably weaker
than that of LaCuO. Our results suggest that the strong correlation
enough to induce Mott gap may not be a prerequisite for the high-
superconductivity.Comment: Scientific Reports (accepted). The values are updated by the
re-calculations of higher accuracy. More parameters now provided in Suppl.
Inf
Robust flat bands in RCo5 (R=rare earth) compounds
The mechanism to realize the peculiar flat bands generally existing in RCo5
(R=rare earth) compounds is clarified by analyzing the first-principles band
structures and the tight-binding model. These flat bands are constructed from
the localized eigenstates, the existence of which is guaranteed by the partial
cancelation between the intersite hopping amplitudes among the Co-3d states at
the Kagome sites and those between the Kagome and honeycomb sites. Their
relative positions to other bands can be controlled by varying the lattice
parameters keeping their dispersion almost flat, which suggests the possibility
of flat-band engineering.Comment: 6 pages, 5 figure