1,990 research outputs found
Ab initio GW many-body effects in graphene
We present an {\it ab initio} many-body GW calculation of the self-energy,
the quasiparticle band plot and the spectral functions in free-standing undoped
graphene. With respect to other approaches, we numerically take into account
the full ionic and electronic structure of real graphene and we introduce
electron-electron interaction and correlation effects from first principles.
Both non-hermitian and also dynamical components of the self-energy are fully
taken into account. With respect to DFT-LDA, the Fermi velocity is
substantially renormalized and raised by a 17%, in better agreement with
magnetotransport experiments. Furthermore, close to the Dirac point the linear
dispersion is modified by the presence of a kink, as observed in ARPES
experiments. Our calculations show that the kink is due to low-energy single-particle excitations and to the plasmon. Finally, the GW
self-energy does not open the band gap.Comment: 5 pages, 4 figures, 1 tabl
Self-consistent Green function approach for calculations of electronic structure in transition metals
We present an approach for self-consistent calculations of the many-body
Green function in transition metals. The distinguishing feature of our approach
is the use of the one-site approximation and the self-consistent quasiparticle
wave function basis set, obtained from the solution of the Schrodinger equation
with a nonlocal potential. We analyze several sets of skeleton diagrams as
generating functionals for the Green function self-energy, including GW and
fluctuating exchange sets. Their relative contribution to the electronic
structure in 3d-metals was identified. Calculations for Fe and Ni revealed
stronger energy dependence of the effective interaction and self-energy of the
d-electrons near the Fermi level compared to s and p electron states.
Reasonable agreement with experimental results is obtained
Ab-initio self-energy corrections in systems with metallic screening
The calculation of self-energy corrections to the electron bands of a metal
requires the evaluation of the intraband contribution to the polarizability in
the small-q limit. When neglected, as in standard GW codes for semiconductors
and insulators, a spurious gap opens at the Fermi energy. Systematic methods to
include intraband contributions to the polarizability exist, but require a
computationally intensive Fermi-surface integration. We propose a numerically
cheap and stable method, based on a fit of the power expansion of the
polarizability in the small-q region. We test it on the homogeneous electron
gas and on real metals such as sodium and aluminum.Comment: revtex, 14 pages including 5 eps figures v2: few fixe
Yambo: an \textit{ab initio} tool for excited state calculations
{\tt yambo} is an {\it ab initio} code for calculating quasiparticle energies
and optical properties of electronic systems within the framework of many-body
perturbation theory and time-dependent density functional theory. Quasiparticle
energies are calculated within the approximation for the self-energy.
Optical properties are evaluated either by solving the Bethe--Salpeter equation
or by using the adiabatic local density approximation. {\tt yambo} is a
plane-wave code that, although particularly suited for calculations of periodic
bulk systems, has been applied to a large variety of physical systems. {\tt
yambo} relies on efficient numerical techniques devised to treat systems with
reduced dimensionality, or with a large number of degrees of freedom. The code
has a user-friendly command-line based interface, flexible I/O procedures and
is interfaced to several publicly available density functional ground-state
codes.Comment: This paper describes the features of the Yambo code, whose source is
available under the GPL license at www.yambo-code.or
Band structures of rare gas solids within the GW approximation
Band structures for solid rare gases (Ne, Ar) have been calculated using the
GW approximation. All electron and pseudopotential ab initio calculations were
performed using Gaussian orbital basis sets and the dependence of particle-hole
gaps and electron affinities on basis set and treatment of core electrons is
investigated. All electron GW calculations have a smaller particle-hole gap
than pseudopotential GW calculations by up to 0.2 eV. Quasiparticle electron
and hole excitation energies, valence band widths and electron affinities are
generally in very good agreement with those derived from optical absorption and
photoemission measurements.Comment: 7 pages 1 figur
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