1,215 research outputs found
TRIQS/CTHYB: A Continuous-Time Quantum Monte Carlo Hybridization Expansion Solver for Quantum Impurity Problems
We present TRIQS/CTHYB, a state-of-the art open-source implementation of the
continuous-time hybridisation expansion quantum impurity solver of the TRIQS
package. This code is mainly designed to be used with the TRIQS library in
order to solve the self-consistent quantum impurity problem in a multi-orbital
dynamical mean field theory approach to strongly-correlated electrons, in
particular in the context of realistic calculations. It is implemented in C++
for efficiency and is provided with a high-level Python interface. The code is
ships with a new partitioning algorithm that divides the local Hilbert space
without any user knowledge of the symmetries and quantum numbers of the
Hamiltonian. Furthermore, we implement higher-order configuration moves and
show that such moves are necessary to ensure ergodicity of the Monte Carlo in
common Hamiltonians even without symmetry-breaking.Comment: 19 pages, this is a companion article to that describing the TRIQS
librar
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Improved wave functions for quantum Monte Carlo
Quantum Monte Carlo (QMC) methods can yield highly accurate energies
for correlated quantum systems. QMC calculations based on many-body
wave functions are considerably more accurate than density
functional theory methods, and their accuracy rivals that of
the most sophisticated quantum chemistry methods. This thesis
is concerned with the development of improved wave function
forms and their use in performing highly-accurate quantum Monte
Carlo calculations.
All-electron variational and diffusion Monte Carlo (VMC and DMC)
calculations are performed for the first-row atoms and
singly-positive ions. Over 98% of the correlation energy
is retrieved at the VMC level and over 99% at the DMC level
for all the atoms and ions. Their first ionization potentials
are calculated within chemical accuracy. Scalar relativistic
corrections to the energies, mass-polarization terms, and one-
and two-electron expectation values are also evaluated. A form
for the electron and intracule densities is presented and fits
to this form are performed.
Typical Jastrow factors used in quantum Monte Carlo calculations
comprise electron-electron, electron-nucleus and
electron-electron-nucleus terms. A general Jastrow factor
capable of correlating an arbitrary of number of electrons and
nuclei, and including anisotropy is outlined. Terms that depend
on the relative orientation of electrons are also introduced and
applied. This Jastrow factor is applied to electron gases, atoms
and molecules and is found to give significant improvement at
both VMC and DMC levels.
Similar generalizations to backflow transformations will
allow useful additional variational freedom in the wave
function. In particular, the use of different backflow functions
for different orbitals is expected to be important in systems
where the orbitals are qualitatively different. The modifications
to the code necessary to accommodate orbital-dependent backflow
functions are described and some systems in which they are
expected to be important are suggested
TRIQS: A Toolbox for Research on Interacting Quantum Systems
We present the TRIQS library, a Toolbox for Research on Interacting Quantum
Systems. It is an open-source, computational physics library providing a
framework for the quick development of applications in the field of many-body
quantum physics, and in particular, strongly-correlated electronic systems. It
supplies components to develop codes in a modern, concise and efficient way:
e.g. Green's function containers, a generic Monte Carlo class, and simple
interfaces to HDF5. TRIQS is a C++/Python library that can be used from either
language. It is distributed under the GNU General Public License (GPLv3).
State-of-the-art applications based on the library, such as modern quantum
many-body solvers and interfaces between density-functional-theory codes and
dynamical mean-field theory (DMFT) codes are distributed along with it.Comment: 27 page
Renormalization of effective interactions in a negative charge-transfer insulator
We compute from first principles the effective interaction parameters
appropriate for a low-energy description of the rare-earth nickelate
LuNiO involving the partially occupied states only. The calculation
uses the constrained random-phase approximation and reveals that the effective
on-site Coulomb repulsion is strongly reduced by screening effects involving
the oxygen- and nickel- states. The long-range component of the
effective low-energy interaction is also found to be sizeable. As a result, the
effective on-site interaction between parallel-spin electrons is reduced down
to a small negative value. This validates effective low-energy theories of
these materials proposed earlier. Electronic structure methods combined with
dynamical mean-field theory are used to construct and solve an appropriate
low-energy model and explore its phase diagram as a function of the on-site
repulsion and Hund's coupling. For the calculated values of these effective
interactions we find, in agreement with experiments, that LuNiO is a
metal without disproportionation of the occupancy when considered in its
orthorhombic structure, while the monoclinic phase is a disproportionated
insulator.Comment: 10 pages, 4 figure
Evaluation of endometrium by transvaginal ultrasonography and hysteroscopy and its correlation with histopathology in perimenopausal women with abnormal uterine bleeding at tertiary rural centre
Background: Abnormal uterine bleeding is one of the commonest clinical presentation ac-counts for 33% gynaecological consultations and this proportion rises to 70% in perimenopausal and postmenopausal age group in any gynaecology clinic. The most probable etiology of abnormal uterine bleeding relates to the patients reproductive age. Various diagnostic techniques have been evolved over the periods to determine the etiology of abnormal uterine bleeding in perimenopausal women, but their accuracy has not been compared properly. The aim of study is to evaluate the endometrium by transvaginal ultrasonography and hysteroscopy and its correlation with histopathology in perimenopausal patients with abnormal uterine bleeding.Methods: Total 96 patients in perimenopausal age group, admitted with chief complaints of ab-normal uterine bleeding were included. All patients underwent transvaginal ultrasonography and hysteroscopy, followed by hysteroscopy guided biopsy and histopathological examination. Accuracy, sensitivity, specificity, positive predictive value and negative predictive value were calculated for both methods and compared, considering histopathological diagnosis as gold standard.Results: Mean age of patients was 44.05±3.29. Hysteroscopy has high accuracy, sensitivity, specificity, positive predictive value and negative predictive value than Transvaginal sonography for diagnosis of all endometrial and intrauterine pathologies.Conclusions: Hysteroscopy results are more consistent with the results of histopathology. Hysteroscopy and hysteroscopy guided biopsy has been proven as gold standard for endometrial evaluation of patients with abnormal uterine bleeding. TVS can be used as most cost effective first step investigation in cases of perimenopausal bleeding
Pagetâs Disease of Maxilla: A Case Report
Paget disease of bone (PDB) is an idiopathic, chronic progressive disease of the bone, characterized by disordered pattern of bone resorption and formation. It has been observed to manifest itself as both monostotic and polyostotic disease. The scientific literature does not report a lot of cases on the incidence of this disease involving the jaws. In India, however a few cases have been reported in the recent times. Pagetâs disease manifests itself as an asymptomatic disorder until it progresses onto the advanced stage where it becomes painful. Thus, its diagnosis on radiographs in the early stage is of paramount importance in order to deter its complications which may not only end up in disability but also can be fatal to life
TRIQS/DFTTools: A TRIQS application for ab initio calculations of correlated materials
We present the TRIQS/DFTTools package, an application based on the TRIQS
library that connects this toolbox to realistic materials calculations based on
density functional theory (DFT). In particular, TRIQS/DFTTools together with
TRIQS allows an efficient implementation of DFT plus dynamical mean-field
theory (DMFT) calculations. It supplies tools and methods to construct Wannier
functions and to perform the DMFT self-consistency cycle in this basis set.
Post-processing tools, such as band-structure plotting or the calculation of
transport properties are also implemented. The package comes with a fully
charge self-consistent interface to the Wien2k band structure code, as well as
a generic interface that allows to use TRIQS/DFTTools together with a large
variety of DFT codes. It is distributed under the GNU General Public License
(GPLv3).Comment: 18 pages, 6 figures, Comp. Phys. Comm. accepted versio
A Radial Velocity Study of the Planetary System of pi Mensae: Improved Planet Parameters for pi Mensae c and a Third Planet on a 125 Day Orbit
Ï Men hosts a transiting planet detected by the Transiting Exoplanet Survey Satellite space mission and an outer planet in a 5.7 yr orbit discovered by radial velocity (RV) surveys. We studied this system using new RV measurements taken with the HARPS spectrograph on ESO's 3.6 m telescope, as well as archival data. We constrain the stellar RV semiamplitude due to the transiting planet, Ï Men c, as Kc = 1.21 ± 0.12 m s^{â1}, resulting in a planet mass of M_{c} = 3.63 ± 0.38 M_{â}. A planet radius of R_{c} = 2.145 ± 0.015 R_{â} yields a bulk density of Ïc = 2.03 ± 0.22 g cm^{â3}. The precisely determined density of this planet and the brightness of the host star make Ï Men c an excellent laboratory for internal structure and atmospheric characterization studies. Our HARPS RV measurements also reveal compelling evidence for a third body, Ï Men d, with a minimum mass M_{d} sin i_{d} = 13.38 ± 1.35 M_{â} orbiting with a period of Porb,d = 125 days on an eccentric orbit (e_{d} = 0.22). A simple dynamical analysis indicates that the orbit of Ï Men d is stable on timescales of at least 20 Myr. Given the mutual inclination between the outer gaseous giant and the inner rocky planet and the presence of a third body at 125 days, Ï Men is an important planetary system for dynamical and formation studies
TOI-2046b, TOI-1181b, and TOI-1516b, three new hot Jupiters from TESS: planets orbiting a young star, a subgiant, and a normal star
We present the confirmation and characterization of three hot Jupiters, TOI-1181b, TOI-1516b, and TOI-2046b, discovered by the TESS space mission. The reported hot Jupiters have orbital periods between 1.4 and 2.05 d. The masses of the three planets are 1.18 ± 0.14 MJ, 3.16 ± 0.12âMJ, and 2.30 ± 0.28 MJ, for TOI-1181b, TOI-1516b, and TOI-2046b, respectively. The stellar host of TOI-1181b is a F9IV star, whereas TOI-1516b and TOI-2046b orbit F main sequence host stars. The ages of the first two systems are in the range of 2â5 Gyrs. However, TOI-2046 is among the few youngest known planetary systems hosting a hot Jupiter, with an age estimate of 100â400 Myrs. The main instruments used for the radial velocity follow-up of these three planets are located at OndĆejov, Tautenburg, and McDonald Observatory, and all three are mounted on 2â3 m aperture telescopes, demonstrating that mid-aperture telescope networks can play a substantial role in the follow-up of gas giants discovered by TESS and in the future by PLATO
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