1,521 research outputs found
High-precision molecular dynamics simulation of UO2-PuO2: pair potentials comparison in UO2
Our series of articles is devoted to high-precision molecular dynamics
simulation of mixed actinide-oxide (MOX) fuel in the approximation of rigid
ions and pair interactions (RIPI) using high-performance graphics processors
(GPU). In this first article 10 most recent and widely used interatomic sets of
pair potentials (SPP) are assessed by reproduction of solid phase properties of
uranium dioxide (UO2) - temperature dependences of the lattice constant, bulk
modulus, enthalpy and heat capacity. Measurements were performed with 1K
accuracy in a wide temperature range from 300K up to melting points. The best
results are demonstrated by two recent SPPs MOX-07 and Yakub-09, which both had
been fitted to the recommended thermal expansion in the range of temperatures
300-3100K. They reproduce the experimental data better than the widely used
SPPs Basak-03 and Morelon-03 at temperatures above 2500K.Comment: 11 pages, 9 figures, 4 table
Electronic structure of FeSe monolayer superconductors
We review a variety of theoretical and experimental results concerning
electronic band structure of superconducting materials based on FeSe
monolayers. Three type of systems are analyzed: intercalated FeSe systems
A_xFe_2Se_{2-x}S_x and [Li_{1-x}Fe_xOH]FeSe as well as the single FeSe layer
films on SrTiO_3 substrate. We present the results of detailed first principle
electronic band structure calculations for these systems together with
comparison with some experimental ARPES data. The electronic structure of these
systems is rather different from that of typical FeAs superconductors, which is
quite significant for possible microscopic mechanism of superconductivity. This
is reflected in the absence of hole pockets of the Fermi surface at
\Gamma-point in Brillouin zone, so that there are no "nesting" properties of
different Fermi surface pockets. LDA+DMFT calculations show that correlation
effects on Fe-3d states in the single FeSe layer are not that strong as in most
of FeAs systems. As a result, at present there is no theoretical understanding
of the formation of rather "shallow" electronic bands at M points. LDA
calculations show that the main difference in electronic structure of FeSe
monolayer on SrTiO_3 substrate from isolated FeSe layer is the presence of the
band of O-2p surface states of TiO_2 layer on the Fermi level together with
Fe-3d states, which may be important for understanding the enhanced T_c values
in this system. We briefly discuss the implications of our results for
microscopic models of superconductivity.Comment: 21 pages, 13 figures, minor typos correcte
On Microscopic Origin of Integrability in Seiberg-Witten Theory
We discuss microscopic origin of integrability in Seiberg-Witten theory,
following mostly the results of hep-th/0612019, as well as present their
certain extension and consider several explicit examples. In particular, we
discuss in more detail the theory with the only switched on higher perturbation
in the ultraviolet, where extra explicit formulas are obtained using
bosonization and elliptic uniformization of the spectral curve.Comment: 24 pages, 1 figure, LaTeX, based on the talks at 'Geometry and
Integrability in Mathematical Physics', Moscow, May 2006; 'Quarks-2006',
Repino, May 2006; Twente conference on Lie groups, December 2006 and
'Classical and Quantum Integrable Models', Dubna, January 200
First Principle Electronic Model for High-Temperature Superconductivity
Using the structural data of the La2CuO4 compound both in the low temperature
tetragonal phase and in the isotropic phase we have derived an effective t-J
model with hoppings t and superexchange interactions J extended up to fourth
and second neareast neighbors respectively. By numerically studying this
hamiltonian we have then reproduced the main experimental features of this HTc
compound: d-wave superconductivity is stabilized at small but finite doping
delta>6% away from the antiferromagnetic region and some evidence of dynamical
stripes is found at commensurate filling 1/8.Comment: 4 pages including 4 figures and 2 table
Quantum Foam and Topological Strings
We find an interpretation of the recent connection found between topological
strings on Calabi-Yau threefolds and crystal melting: Summing over statistical
mechanical configuration of melting crystal is equivalent to a quantum
gravitational path integral involving fluctuations of Kahler geometry and
topology. We show how the limit shape of the melting crystal emerges as the
average geometry and topology of the quantum foam at the string scale. The
geometry is classical at large length scales, modified to a smooth limit shape
dictated by mirror geometry at string scale and is a quantum foam at area
scales g_s \alpha'.Comment: 55 page
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