### 604 results

Contributors: Naoya Chikano, Kazuyoshi Yoshimi, Junya Otsuki, Hiroshi Shinaoka

Date: 2019-03-22

... The open-source library, irbasis, provides easy-to-use tools for two sets of orthogonal functions named intermediate representation (IR). The IR basis enables a compact representation of the Matsubara Green’s function and efficient calculations of quantum models. The IR basis functions are defined as the solution of an integral equation whose analytical solution is not available for this moment. The library consists of a database of pre-computed high-precision numerical solutions and computational code for evaluating the functions from the database. This paper describes technical details and demonstrates how to use the library.

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Contributors: Gianluca Prandini, Mario Galante, Nicola Marzari, Paolo Umari

Date: 2019-03-22

... We present SIMPLE, a code developed to calculate optical properties of metallic and insulating extended systems using the optimal basis method originally proposed by E. L. Shirley in 1996. Two different approaches for the evaluation of the complex dielectric function are implemented: (i) the independent-particle approximation considering both interband and intraband contributions for metals and (ii) the Bethe–Salpeter equation for insulators. Since, notably, the optimal basis set is systematically improvable, accurate results can be obtained at a strongly reduced computational cost. Moreover, the simplicity of the method allows for a straightforward use of the code; improvement of the optimal basis and thus the overall precision of the simulations is simply controlled by one (for metals) or two (for insulators) input thresholds. The code is extensively tested, in terms of verification and performance, on bulk silver for metals and on bulk silicon for insulators.

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Contributors: Meisam Farzalipour Tabriz, Bálint Aradi, Thomas Frauenheim, Peter Deák

Date: 2019-03-22

... The surface of solids or their interface with the gas phase is often modelled by a slab, periodic in two dimensions and repeated artificially in the third. When studying charged systems, a compensating background charge is required to avoid the divergence of the Coulomb energy. However, the interactions between the periodic images of the localized charge and between the localized charge and its neutralizing background can cause significant errors in the total energy. We have implemented the correction scheme proposed by Komsa and Pasquarello (2013), which estimates the error in the total energy by modelling the distribution of the localized extra charge with Gaussian functions at different sites, and comparing its energy in the periodic and in the isolated case. The program is user-friendly and robust, it is automated for simple cases while keeping the flexibility for the advanced users to handle non-trivial ones.

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Contributors: Francesc Salvat, José M. Fernández-Varea

Date: 2019-03-22

... The Fortran subroutine package radial for the numerical solution of the Schrödinger and Dirac wave equations of electrons in central potentials is described. The considered potentials V(r) are such that the function ${\cal V}(r) \equiv rV(r)$ is finite for all r and tends to constant values when r -> 0 and r -> infinity. This includes finite-range potentials as well as combinations of Coulomb and finite-range potentials. The function ${\cal V}(r)$ used in the numerical calculation is the natural cubic spline that interpolates a table of values provided by the user. The radial wave equations are solved by using piecewise exact power series expansions of the radial functions, which are summed up to the prescribed accuracy so that truncation errors can be completely avoided. The radial subroutines compute radial wave functions, eigenvalues for bound states and phase shifts for free states. Specific subroutines are also provided for computing the radial functions and phase shifts for free states of complex optical potentials having a finite-range absorptive imaginary part. The solution subroutines are accompanied by example main programs, as well as with specific programs that perform calculations relevant in atomic, nuclear, and radiation physics (the self-consistent solution of the Dirac–Hartee–Fock–Slater equations for neutral atoms and positive ions, and the calculation of cross sections for elastic scattering of high-energy electrons and positrons by atoms and of nucleons by nuclei). The distribution package includes a detailed manual with a description of the basic physics and the mathematical formulas implemented in the subroutines.

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Contributors: Jerzy Goraus

Date: 2019-03-22

... Specific heat of rare-earth based materials at low temperatures can often be described by the Schotte–Schotte model for Kondo impurity. For several decades thousands of papers have been published which were devoted to physics of rare-earth based compounds and often presented specific heat measurements for Kondo systems. The Schotte–Schotte model for Kondo impurity in a magnetic field requires evaluation of trigamma function for complex argument values. Typical graphing software for general use does not provide such capability. Therefore, very few papers related to Kondo effect in rare-earth based compounds provided analysis within that model. In this report we present a web page which fits specific heat data with a sum of electronic, lattice and Schotte–Schotte terms. The interface is written in Javascript, whereas back-end fitting engine is written in C and compiled to Javascript asm.js code using Emscripten compiler.

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Contributors: L. Hayen, N. Severijns

Date: 2019-03-22

... Several searches for Beyond Standard Model physics rely on an accurate and highly precise theoretical description of the allowed beta spectrum. Following recent theoretical advances, a C++ implementation of an analytical description of the allowed beta spectrum shape was constructed. It implements all known corrections required to give a theoretical description accurate to a few parts in 10^4 . The remaining nuclear structure-sensitive input can optionally be calculated in an extreme single-particle approximation with a variety of nuclear potentials, or obtained through an interface with more state-of-the-art computations. Due to its relevance in modern neutrino physics, the corresponding (anti)neutrino spectra are readily available with appropriate radiative corrections. In the interest of user-friendliness, a graphical interface was developed in Python with a coupling to a variety of nuclear databases. We present several test cases and illustrate potential usage of the code. Our work can be used as the foundation for current and future high-precision experiments related to the beta decay process.

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Contributors: S. Borowka, G. Heinrich, S. Jahn, S. P. Jones, M. Kerner, J. Schlenk

Date: 2019-03-19

... The purely numerical evaluation of multi-loop integrals and amplitudes can be a viable alternative to analytic approaches, in particular in the presence of several mass scales, provided sufficient accuracy can be achieved in an acceptable amount of time. For many multi-loop integrals, the fraction of time required to perform the numerical integration is significant and it is therefore beneficial to have efficient and well-implemented numerical integration methods. With this goal in mind, we present a new stand-alone integrator based on the use of (quasi-Monte Carlo) rank-1 shifted lattice rules. For integrals with high variance we also implement a variance reduction algorithm based on fitting a smooth function to the inverse cumulative distribution function of the integrand dimension-by-dimension. Additionally, the new integrator is interfaced to pySecDec to allow the straightforward evaluation of multi-loop integrals and dimensionally regulated parameter integrals. In order to make use of recent advances in parallel computing hardware, our integrator can be used both on CPUs and CUDA compatible GPUs where available.

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Contributors: A. Cuoci, A. Frassoldati, T. Faravelli, E. Ranzi

Date: 2019-03-14

... This program has been imported from the CPC Program Library held at Queen's University Belfast (1969-2018) Abstract OpenSMOKE++ is a general framework for numerical simulations of reacting systems with detailed kinetic mechanisms, including thousands of chemical species and reactions. The framework is entirely written in object-oriented C++ and can be easily extended and customized by the user for specific systems, without having to modify the core functionality of the program. The OpenSMOKE++ framework can handle simulations of ideal chemical reactors (plug-flow, batch, and jet stirred reactors), shock-tu... Title of program: OpenSMOKE++ Catalogue Id: AEVY_v1_0 Nature of problem Evolution of reacting gas mixtures with detailed description of thermodynamic, kinetic and transport data. Versions of this program held in the CPC repository in Mendeley Data AEVY_v1_0; OpenSMOKE++; 10.1016/j.cpc.2015.02.014

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Contributors: A. Otero-de-la-Roza, David Abbasi-Pérez, Víctor Luaña

Date: 2019-03-14

... This program has been imported from the CPC Program Library held at Queen's University Belfast (1969-2018) Abstract In the second article of the series, we present the Gibbs2 code, a Fortran90 reimplementation of the original Gibbs program [Comput. Phys. Commun. 158 (2004) 57] for the calculation of pressure–temperature dependent thermodynamic properties of solids under the quasiharmonic approximation. We have taken advantage of the detailed analysis carried out in the first paper to implement robust fitting techniques. In addition, new models to introduce temperature effects have been incorporated, from ... Title of program: Gibbs2 Catalogue Id: AEJI_v1_0 Nature of problem Given the static E(V) curve, and possibly vibrational information such as the phonon density of states, calculate the equilibrium volume and thermodynamic properties of a solid at arbitrary temperatures and pressures in the framework of the quasiharmonic approximation. Versions of this program held in the CPC repository in Mendeley Data AEJI_v1_0; Gibbs2; 10.1016/j.cpc.2011.05.009

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Contributors: Simon Badger, Benedikt Biedermann, Peter Uwer, Valery Yundin

Date: 2019-03-14

... This program has been imported from the CPC Program Library held at Queen's University Belfast (1969-2018) Abstract We present a C++ library for the numerical evaluation of one-loop virtual corrections to multi-jet production in massless QCD. The pure gluon primitive amplitudes are evaluated using NGluon (Badger et al., (2011) [62]). A generalized unitarity reduction algorithm is used to construct arbitrary multiplicity fermion–gluon primitive amplitudes. From these basic building blocks the one-loop contribution to the squared matrix element, summed over colour and helicities, is calculated. No approximat... Title of program: NJET Catalogue Id: AEPF_v1_0 Nature of problem Evaluation of virtual corrections for multi-jet production in massless QCD Versions of this program held in the CPC repository in Mendeley Data AEPF_v1_0; NJET; 10.1016/j.cpc.2013.03.018

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