20 research outputs found
Quasiparticle self-consistent method; a basis for the independent-particle approximation
We have developed a new type of self-consistent scheme within the
approximation, which we call quasiparticle self-consistent (QS). We
have shown that QS rather well describes energy bands for a wide-range of
materials, including many where the local-density approximation fails. QS
contains physical effects found in other theories such as LDA, SIC and
in a satisfactory manner without many of their drawbacks (partitioning of
itinerant and localized electrons, adjustable parameters, ambiguities in
double-counting, etc.). We present some theoretical discussion concerning the
formulation of QS, including a prescriptino for calculating the total
energy. We also address several key methodological points needed for
implementation. We then show convergence checks and some representative results
in a variety of materials.Comment: v2:the same as previous version --but better tex file; v3:add
appendix and modify introduction,mainly; v4 mainly, theoretical section (IB
IC) are renewe
All-electron self-consistent GW approximation: Application to Si, MnO, and NiO
We present a new kind self-consistent GW approximation (scGW) based on the
all-electron, full-potential LMTO method. By iterating the eigenfunctions of
the GW Hamiltonian, self-consistency in both the charge density and the
quasiparticle spectrum is achieved. We explain why this form of
self-consistency should be preferred to the conventional one. Then some results
for Si are shown as a representative semiconductor, to establish agreement with
a prior scGW calculation. Finally we consider many details in the electronic
structure of the antiferromagnetic insulators MnO and NiO. Excellent agreement
with experiment is shown for many properties, suggesting that a Landau
quasiparticle (energy band) picture of MnO and NiO provides a reasonable
description of electronic structure even in these correlated materials.Comment: 5 pages, 3 figure
Adequacy of Approximations in GW Theory
We use an all-electron implementation of the GW approximation to analyze
several possible sources of error in the theory and its implementation. Among
these are convergence in the polarization and Green's functions, the dependence
of QP levels on choice of basis sets, and differing approximations for dealing
with core levels. In all GW calculations presented here, G and W are generated
from the local-density approximation (LDA), which we denote as the \GLDA\WLDA
approximation. To test its range of validity, the \GLDA\WLDA approximation is
applied to a variety of materials systems. We show that for simple sp
semiconductors, \GLDA\WLDA always underestimates bandgaps; however, better
agreement with experiment is obtained when the self-energy is not renormalized,
and we propose a justification for it. Some calculations for Si are compared to
pseudopotential-based \GLDA\WLDA calculations, and some aspects of the
suitability of pseudopotentials for GW calculations are discussed.Comment: 38 pages,6 figures. Minor Revision
Theory of enhancement of thermoelectric properties of materials with nanoinclusions
Based on the concept of band bending at metal/semiconductor interfaces as an
energy filter for electrons, we present a theory for the enhancement of the
thermoelectric properties of semiconductor materials with metallic
nanoinclusions. We show that the Seebeck coefficient can be significantly
increased due to a strongly energy-dependent electronic scattering time. By
including phonon scattering, we find that the enhancement of ZT due to electron
scattering is important for high doping, while at low doping it is primarily
due to a decrease in the phonon thermal conductivity