948 research outputs found
Self-Consistent Green Function Embedding for Advanced Electronic Structure Methods Based on a Dynamical Mean-Field Concept
We present an embedding scheme for periodic systems that facilitates the
treatment of the physically important part (here the unit cell) with advanced
electronic-structure methods, that are computationally too expensive for
periodic systems. The rest of the periodic system is treated with
computationally less demanding approaches, e.g., Kohn-Sham density-functional
theory, in a self- consistent manner. Our scheme is based on the concept of
dynamical mean-field theory (DMFT) formulated in terms of Green functions. In
contrast to the original DMFT formulation for correlated model Hamiltonians, we
here consider the unit cell as local embedded cluster in a first-principles
way, that includes all electronic degrees of freedom. Our real-space dynamical
mean-field embedding (RDMFE) scheme features two nested Dyson equations, one
for the embedded cluster and another for the periodic surrounding. The total
energy is computed from the resulting Green functions. The performance of our
scheme is demonstrated by treating the embedded region with hybrid functionals
and many-body perturbation theory in the GW approach for simple bulk systems.
The total energy and the density of states converge rapidly with respect to the
computational parameters and approach their bulk limit with increasing cluster
(i.e., unit cell) size
Lack of neurosteroid selectivity at δ vs. γ2-containing GABAA receptors in dentate granule neurons
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Renormalized Second-order Perturbation Theory for The Electron Correlation Energy: Concept, Implementation, and Benchmarks
We present a renormalized second-order perturbation theory (rPT2), based on a
Kohn-Sham (KS) reference state, for the electron correlation energy that
includes the random-phase approximation (RPA), second-order screened exchange
(SOSEX), and renormalized single excitations (rSE). These three terms all
involve a summation of certain types of diagrams to infinite order, and can be
viewed as "renormalization" of the 2nd-order direct, exchange, and single
excitation (SE) terms of Rayleigh-Schr\"odinger perturbation theory based on an
KS reference. In this work we establish the concept of rPT2 and present the
numerical details of our SOSEX and rSE implementations. A preliminary version
of rPT2, in which the renormalized SE (rSE) contribution was treated
approximately, has already been benchmarked for molecular atomization energies
and chemical reaction barrier heights and shows a well balanced performance
[Paier et al, New J. Phys. 14, 043002 (2012)]. In this work, we present a
refined version of rPT2, in which we evaluate the rSE series of diagrams
rigorously. We then extend the benchmark studies to non-covalent interactions,
including the rare-gas dimers, and the S22 and S66 test sets. Despite some
remaining shortcomings, we conclude that rPT2 gives an overall satisfactory
performance across different chemical environments, and is a promising step
towards a generally applicable electronic structure approach.Comment: 16 pages, 11 figure
Density-functional Theory for f electron Systems: the {\alpha}-{\gamma} Phase Transition in Cerium
The isostructural {\alpha}-{\gamma} phase transition in cerium is analyzed
using density-functional theory with different exchange-correlation
functionals, in particular the PBE0 hybrid functional and the exact- exchange
plus correlation in the random-phase approximation [(EX+cRPA)@PBE0] approach.
We show that the Hartree-Fock exchange part of the hybrid functional actuates
two distinct solutions at zero temperature that can be associated with the
{\alpha} and {\gamma} phases of cerium. However, despite the relatively good
structural and magnetic properties, PBE0 predicts the {\gamma} phase to be the
stable phase at ambient pressure and zero temperature, in contradiction with
low temperature experiments. EX+cRPA reverses the energetic ordering, which
emphasizes the importance of correlation for rare- earth systems
Unified description of ground and excited states of finite systems: the self-consistent GW approach
GW calculations with fully self-consistent G and W -- based on the iterative
solution of the Dyson equation -- provide an approach for consistently
describing ground and excited states on the same quantum mechanical level. We
show that for the systems considered here self-consistent GW reaches the same
final Green function regardless of the initial reference state.
Self-consistency systematically improves ionization energies and total energies
of closed shell systems compared to G_0W_0 based on Hartree-Fock and
(semi)local density-functional theory. These improvements also translate to the
electron density as exemplified by an improved description of dipole moments
and permit us to assess the quality of ground state properties such as bond
lengths and vibrational frequencies.Comment: 5 pages, 4 figures, supplemental materia
Evolution and potential function of fibrinogen-like domains across twelve Drosophila species
<p>Abstract</p> <p>Background</p> <p>The fibrinogen-like (FBG) domain consists of approximately 200 amino acid residues, which has high sequence similarity to the C-terminal halves of fibrinogen β and γ chains. Fibrinogen-related proteins (FREPs) containing one or more FBG domains are found universally in vertebrates and invertebrates. In invertebrates, FREPs are involved in immune responses and other aspects of physiology. To understand the complexity of this gene family in <it>Drosophila</it>, we analyzed FREPs in twelve <it>Drosophila </it>species.</p> <p>Results</p> <p>Using the genome data from 12 <it>Drosophila </it>species, we identified FBG domains in each species. The results show that the gene numbers in each species vary from 14 genes up to 43 genes. Using sequence profile analysis, we found that FBG domains have high sequence similarity and are highly conserved throughout. By comparison of structure and sequence conservation, some of the FBG domains in <it>Drosophila melanogaster </it>are predicted to function in recognition of carbohydrates and their derivatives on the surface of microorganisms in innate immunity.</p> <p>Conclusion</p> <p>Sequence and structural analyses show that FREP family across 12 <it>Drosophila </it>species contains conserved FBG domains. Expansion of the FREP families in <it>Drosophila </it>is mainly accounted by a major expansion of FBG domains.</p
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