3,255 research outputs found
Calculating DMFT forces in ab-initio ultrasoft pseudopotential formalism
In this paper, we show how to calculate analytical atomic forces within
self-consistent density functional theory + dynamical mean-field theory
(DFT+DMFT) approach in the case when ultra-soft or norm-conserving
pseudopotentials are used. We show how to treat the non-local projection terms
arising within the pseudopotential formalism and circumvent the problem of
non-orthogonality of the Kohn-Sham eigenvectors. Our approach is, in principle,
independent of the DMFT solver employed, and here was tested with the Hubbard I
solver. We benchmark our formalism by comparing against the forces calculated
in CeO and PrO by numerical differentiation of the total free
energy, as well as by comparing the energy profiles against the numerically
integrated analytical forces.Comment: 12 pages, 3 figure
Characterizing and Overcoming Surface Paramagnetism in Magnetoelectric Antiferromagnets
We use a combination of density functional theory and Monte Carlo
calculations to calculate the surface magnetization in magnetoelectric
at finite temperatures. Such antiferromagnets, lacking both
inversion and time-reversal symmetries, are required by symmetry to posses an
uncompensated magnetization density on particular surface terminations. Here,
we first show that the uppermost layer of magnetic moments on the
surface remain paramagnetic at the bulk N\'{e}el temperature, bringing the
theoretical estimate of surface magnetization density in line with experiment.
We demonstrate that the lower surface ordering temperature compared to bulk is
a generic feature of surface magnetization when the termination reduces the
effective Heisenberg coupling. We then propose two methods by which the surface
magnetization in could be stabilised at higher temperatures.
Specifically, we show that the effective coupling of surface magnetic ions can
be drastically increased either by a different choice of surface Miller plane,
or by doping. Our findings provide an improved understanding of
surface magnetization properties in AFMs.Comment: Supplementary material included as appendi
Mostly sunny : a forecast of tomorrow's power index research
Power index research has been a very active field in the last decades. Will
this continue or are all the important questions solved? We argue that there
are still many opportunities to conduct useful research with and on power
indices. Positive and normative questions keep calling for theoretical and
empirical attention. Technical and technological improvements are likely to
boost applicability.Comment: 12 page
Species-independent bioassay for sensitive quantification of antiviral type I interferons
<p>Abstract</p> <p>Background</p> <p>Studies of the host response to infection often require quantitative measurement of the antiviral type I interferons (IFN-α/β) in biological samples. The amount of IFN is either determined via its ability to suppress a sensitive indicator virus, by an IFN-responding reporter cell line, or by ELISA. These assays however are either time-consuming and lack convenient readouts, or they are rather insensitive and restricted to IFN from a particular host species.</p> <p>Results</p> <p>An IFN-sensitive, <it>Renilla </it>luciferase-expressing Rift Valley fever virus (RVFV-Ren) was generated using reverse genetics. Human, murine and avian cells were tested for their susceptibility to RVFV-Ren after treatment with species-specific IFNs. RVFV-Ren was able to infect cells of all three species, and IFN-mediated inhibition of viral reporter activity occurred in a dose-dependent manner. The sensitivity limit was found to be 1 U/ml IFN, and comparison with a standard curve allowed to determine the activity of an unknown sample.</p> <p>Conclusions</p> <p>RVFV-Ren replicates in cells of several species and is highly sensitive to pre-treatment with IFN. These properties allowed the development of a rapid, sensitive, and species-independent antiviral assay with a convenient luciferase-based readout.</p
Present-day Mars' seismicity predicted from 3-D thermal evolution models of interior dynamics
©2018. American Geophysical UnionThe Interior Exploration using Seismic Investigations, Geodesy and Heat Transport mission, to be launched in 2018, will perform a comprehensive geophysical investigation of Mars in situ. The Seismic Experiment for Interior Structure package aims to detect global and regional seismic events and in turn offer constraints on core size, crustal thickness, and core, mantle, and crustal composition. In this study, we estimate the present‐day amount and distribution of seismicity using 3‐D numerical thermal evolution models of Mars, taking into account contributions from convective stresses as well as from stresses associated with cooling and planetary contraction. Defining the seismogenic lithosphere by an isotherm and assuming two end‐member cases of 573 K and the 1073 K, we determine the seismogenic lithosphere thickness. Assuming a seismic efficiency between 0.025 and 1, this thickness is used to estimate the total annual seismic moment budget, and our models show values between 5.7 × 1016 and 3.9 × 1019 Nm
Exploring the Effect of the Number of Hydrogen Atoms on the Properties of Lanthanide Hydrides by DMFT
Lanthanide hydrogen-rich materials have long been considered as one of the
candidates with high-temperature superconducting properties in condensed matter
physics, and have attracted great interest. Attempts to investigate the effects
of different compositions of lanthanide hydrogen-rich materials are ongoing,
with predictions and experimental studies in recent years having shown that
substances such as LaH 10 , CeH 9 , and LaH 16 exhibit extremely high
superconducting temperatures between 150-250 GPa. In particular, researchers
have noted that in those materials an increase in the f character at the Fermi
level leads to an increase in the superconducting temperature. Here, we further
elaborate on the effect of the ratios of lanthanide to hydrogen in these
substances with the aim to bring more clarity to the study of superhydrides in
these extreme cases by comparing a variety of lanthanide hydrogen-rich
materials with different ratios using the DMFT method, and provide ideas for
later structural predictions and material property studies.Comment: 7pages, 5figure
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