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In this paper, we develop two-level numerical methods for the time-dependent Schrodinger equation (TDSE) in multi-frequency regime. This work is motivated by attosecond science (Corkum and Krausz, 2007), which refers to the interaction of short and intense laser pulses with quantum particles generating wide frequency spectrum light, and allowing for the coherent emission of attosecond pulses (1 attosecond=10−18 s). The principle of the proposed methods consists in decomposing a wavefunction into a low/moderate frequency (quantum) contribution, and a high frequency contribution exhibiting a semi-classical behavior. Low/moderate frequencies are computed through the direct solution to the quantum TDSE on a coarse mesh, and the high frequency contribution is computed by frozen Gaussian approximation (Herman and Kluk, 1984). This paper is devoted to the derivation of consistent, accurate and efficient algorithms performing such a decomposition and the time evolution of the wavefunction in the multi-frequency regime. Numerical simulations are provided to illustrate the accuracy and efficiency of the derived algorithms.

In this paper we present the Open Software Services for Classrooms and Research (OSSCAR) platform. OSSCAR provides an open collaborative environment to develop, deploy and access educational resources in the form of web applications. To minimize efforts in the creation and use of new educational material, it combines software tools that have emerged as standards with custom domain-specific ones. The technical solutions adopted to create and distribute content are described and motivated on the basis of reliability, sustainability, ease of uptake and use. Examples from courses in the domains of physics, chemistry, and materials science are shown to demonstrate the style and level of interactivity of typical applications. The tools presented are easy to use, and create a uniform and open environment exploitable by a large community of teachers, students, and researchers with the goal of facilitating learning and avoiding, when possible, duplication of efforts in creating teaching material. Contributions to expand the educational content of the OSSCAR project are welcome., Comment: 15 pages, 8 figures

We present a code for the large-scale data analysis of electron cyclotron emission (ECE) measurements from magnetized plasmas called ECRad – the Electron Cyclotron Radiation transport model for Advanced Data analysis. Its key features are low computational cost, high robustness and the capability to predict ECE spectra of plasmas with non-thermal electron populations. This is accomplished by combining the absorption coefficient given by Albajar et al. (2007) and a corresponding emissivity for the radiation transport with geometrical optics ray tracing for the computation of the diagnostic line of sight. Another important aspect of ECRad is that it has passed a large amount of verification tests against real measurements by conventional, oblique and ECE imaging diagnostics. This paper explains the physical model of ECRad and its implementation. Furthermore, it is discussed how the code can be used for the inference of the electron temperature from ECE measurements and how an oblique ECE diagnostic can be cross-calibrated with ECRad.

Relativistic fluid dynamics is a major component in dynamical simulations of the quark-gluon plasma created in relativistic heavy-ion collisions. Simulations of the full three-dimensional dissipative dynamics of the quark-gluon plasma with fluctuating initial conditions are computationally expensive and typically require some degree of parallelization. In this paper, we present a GPU implementation of the Kurganov-Tadmor algorithm which solves the 3+1d relativistic viscous hydrodynamics equations including the effects of both bulk and shear viscosities. We demonstrate that the resulting CUDA-based GPU code is approximately two orders of magnitude faster than the corresponding serial implementation of the Kurganov-Tadmor algorithm. We validate the code using (semi-)analytic tests such as the relativistic shock-tube and Gubser flow., 57 pages, 18 figures

In the paper, gridless particle techniques are presented in order to solve problems involving electrostatic, collisionless plasmas. The method makes use of computational particles having the shape of spherical shells or of rings, and can be used to study cases in which the plasma has spherical or axial symmetry, respectively. As a computational grid is absent, the technique is particularly suitable when the plasma occupies a rapidly changing space region.

Computational physics problems often have a common set of aspects to them that any particular numerical code will have to address. Because these aspects are common to many problems, having a framework already designed and ready to use will not only speed the development of new codes, but also enhance compatibility between codes. Some of the most common aspects of computational physics problems are: a grid, a clock which tracks the flow of the simulation, and a set of models describing the dynamics of various quantities on the grid. Having a framework that could deal with these basic aspects of the simulation in a common way could provide great value to computational scientists by solving various numerical and class design issues that routinely arise. This paper describes the newly developed computational framework that we have built for rapidly prototyping new physics codes. This framework, called turboPy, is a lightweight physics modeling framework based on the design of the particle-in-cell code turboWAVE. It implements a class (called Simulation ) which drives the simulation and manages communication between physics modules, a class (called PhysicsModule ) which handles the details of the dynamics of the various parts of the problem, and some additional classes such as a Grid class and a Diagnostic class to handle various ancillary issues that commonly arise. Program summary Program Title: TurboPy CPC Library link to program files: http://dx.doi.org/10.17632/rznn6s5myw.1 Developer’s repository link: https://github.com/NRL-Plasma-Physics-Division/turbopy Licensing provisions: CC0 1.0 Programming language: Python Nature of problem: Many computation physics problems have a common set of aspects to them that are often addressed in a custom way in every different code, which leads to lengthy and redundant development and testing, as well as introducing roadblocks to interoperability. Solution method: Implement a set of python classes as a lightweight framework that deals with these common problems, so that development time on new computational physics codes is reduced, and interoperability and reusability are increased. References: A.S. Richardson et al., TurboPy: A lightweight computational physics framework. NRL-Plasma-Physics-Division/turbopy (v2020.08.05). doi:10.5281/zenodo.3973693

This paper presents the numerical methods for the nonlinear simulations of cyclokinetic [Waltz and Zhao Deng (2013)] equations in Fourier harmonics of the gyro-phase. A parallel processed, implicit time advanced, Eulerian (or continuum) code (rCYCLO) is developed. A novel numerical treatment of the magnetic moment velocity space derivative operator guarantees accurate conservation of the incremental entropy. By comparing the cyclokinetic simulations with the corresponding gyrokinetics, we quantitatively test the breakdown of gyrokinetics at high turbulence levels over a range of large relative ion cyclotron frequency ( 10 Ω ∗ 100 where Ω ∗ = 1 / ρ ∗ , and ρ ∗ is the relative ion gyroradius). As an important code verification, the rCYCLO gyrokinetic transport recovers cyclokinetic transport at high relative ion cyclotron frequency ( Ω ∗ ⩾ 50 ) and low turbulence levels. In the case of linearly stable ion cyclotron modes, the cyclokinetic transport is lower (not higher) than the gyrokinetic transport at high turbulence levels and low- Ω ∗ values.

Marcin Mazdziarz has published a comment on our recent paper by I. Mosyagin, A.V. Lugovskoy, O.M. Krasilnikov, Yu.Kh. Vekilov, S.I. Simak and L.A. Abrikosov titled "Ab initio calculations of pressure dependence of high-order elastic constants using finite deformations approach" [Computer Physics Communications 220 (2017)2030]. The author states that there are serious fundamental errors and flaws. In this reply we clarify all misunderstanding mentioned in the said comment. (C) 2018 Published by Elsevier B.V. Funding Agencies|Swedish Research Council [2015-04391, 2014-4750]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; Ministry of Education and Science of the Russian Federation [K2-2017-080, 14.Y26.31.0005]

Recently, I. Mosyagin, A.V. Lugovskoy, O.M. Krasilnikov, this http URL. Vekilov, S.I. Simak and I.A. Abrikosov in the paper: "Ab initio calculations of pressure-dependence of high-order elastic constants using finite deformations approach"[Computer Physics Communications 220 (2017) 2030] presented a description of a technique for ab initio calculations of the pressure dependence of second- and third-order elastic constants. Unfortunately, the work contains serious and fundamental flaws in the field of finite-deformation solid mechanics.

Thermal conductivity is a very important property of a material both for testing theoretical models and for designing better practical devices such as more efficient thermoelectrics, and accurate and efficient calculations of thermal conductivity are very desirable. In this paper, we develop a highly efficient molecular dynamics code fully implemented on graphics processing units for thermal conductivity calculations using the Green–Kubo formula. We compare two different schemes for force evaluation, a previously used thread-scheme, where a single thread is used for one particle and each thread calculates the total force for the corresponding particle, and a new block-scheme, where a whole block is used for one particle and each thread in the block calculates one or several pair forces between the particle associated with the given block and its neighbor particle(s) associated with the given thread. For both schemes, two different classical potentials, namely, the Lennard-Jones potential and the rigid-ion potential are implemented. While the thread-scheme performs a little better for relatively large systems, the block-scheme performs much better for relatively small systems. The relative performance of the block-scheme over the thread-scheme also increases with the increasing cutoff radius. We validate the implementation by calculating lattice thermal conductivities of solid argon and lead telluride. The efficiency of our code makes it very promising to study thermal conductivity properties of more complicated materials, especially, materials with interesting nanostructures.

In this paper we describe a new release of the PRESHOWER program, a tool for Monte Carlo simulation of propagation of ultra-high energy photons in the magnetic field of the Earth. The PRESHOWER program is designed to calculate magnetic pair production and bremsstrahlung and should be used together with other programs to simulate extensive air showers induced by photons. The main new features of the PRESHOWER code include a much faster algorithm applied in the procedures of simulating the processes of gamma conversion and bremsstrahlung, update of the geomagnetic field model, and a minor correction. The new simulation procedure increases the flexibility of the code so that it can also be applied to other magnetic field configurations such as, for example, encountered in the vicinity of the sun or neutron stars., 22 pages, 6 figures

Pariser-Parr-Pople (P-P-P) model Hamiltonian is employed frequently to study the electronic structure and optical properties of $\pi$-conjugated systems. In this paper we describe a Fortran 90 computer program which uses the P-P-P model Hamiltonian to solve the Hartree-Fock (HF) equation for infinitely long, one-dimensional, periodic, $\pi$-electron systems. The code is capable of computing the band structure, as also the linear optical absorption spectrum, by using the tight-binding (TB) and the HF methods. Furthermore, using our program the user can solve the HF equation in the presence of a finite external electric field, thereby, allowing the simulation of gated systems. We apply our code to compute various properties of polymers such as $trans$-polyacetylene ($t$-PA), poly-\emph{para}-phenylene (PPP), and armchair and zigzag graphene nanoribbons, in the infinite length limit., Comment: 33 pages, 11 figures (included), submitted for publication

Article history: Received 22 July 2010 Accepted 6 October 2010 Available online xxxx Computational physics as a mode of studying the mathematical and physical sciences has grown world- wide over the past two decades, but this trend is yet to fully develop in Africa. The essential ingredients are there for this to happen: increasing internet connectivity, cheaper computing resources and the widespread availability of open source and freeware. The missing ingredients centre on intellectual isolation and the low levels of quality international collaborations. Low level of funding for research from local governments remains a critical issue. This paper gives a motivation for the importance of developing computational physics at the university undergraduate level, graduate level and research levels and gives suggestions on how this may be achieved within the African context. It is argued that students develop a more intuitive feel for the mathematical and physical sciences, that they learn useful, transferable skills that make our graduates well-sought after in the industrial and commercial environments, and that such graduates are better prepared to tackle research problems at the masters and doctoral levels. At the research level, the case of the African School Series on Electronic Structure Methods and Applications (ASESMA) is presented as a new multi-national modality for engaging with African scientists. There are many novel aspects to this School series, which are discussed. © 2010 Elsevier B.V. All rights reserved.

It has been recently argued through numerical work that rotating stars with a high degree of differential rotation are dynamically unstable against bar-mode deformation, even for values of the ratio of rotational kinetic energy to gravitational potential energy as low as O(0.01). This may have implications for gravitational wave astronomy in high-frequency sources such as core collapse supernovae. In this paper we present high-resolution simulations, performed with an adaptive mesh refinement hydrodynamics code, of such low T/|W| bar-mode instability. The complex morphological features involved in the nonlinear dynamics of the instability are revealed in our simulations, which show that the excitation of Kelvin-Helmholtz-like fluid modes outside the corotation radius of the star leads to the saturation of the bar-mode deformation. While the overall trends reported in an earlier investigation are confirmed by our work, we also find that numerical resolution plays an important role during the long-term, nonlinear behaviour of the instability, which has implications on the dynamics of rotating stars and on the attainable amplitudes of the associated gravitational wave signals., Comment: 20 pages, 9 figures, accepted for publication in Computer Physics Communications.

Neutral beam injection (NBI) will be one of the main sources of heating and non-inductive current drive in ITER. Due to high level of injected power the beam induced heat loads present a potential threat to the integrity of the first wall of the device, particularly in the presence of non-axisymmetric perturbations of the magnetic field. Neutral beam injection can also destabilize Alfven eigenmodes and energetic particle modes, and act as a source of plasma rotation. Therefore, reliable and accurate simulation of NBI is important for making predictions for ITER, as well as for any other current or future fusion device. This paper introduces a new beamlet-based neutral beam ionization model called BBNBI. It takes into account the fine structure of the injector, follows the injected neutrals until ionization, and generates a source ensemble of ionized NBI test particles for slowing down calculations. BBNBI can be used as a stand-alone model but together with the particle following code ASCOT it forms a complete and sophisticated tool for simulating neutral beam injection. The test particle ensembles from BBNBI are found to agree well with those produced by PENCIL for JET, and those produced by NUBEAM both for JET and ASDEX Upgrade plasmas. The first comprehensive comparisons of beam slowing down profiles of interest from BBNBI + ASCOT with results from PENCIL and NUBEAM/TRANSP, for both JET and AUG, are presented. It is shown that, for an axisymmetric plasma, BBNBI + ASCOT and NUBEAM agree remarkably well. Together with earlier 3D studies, these results further validate using BBNBI + ASCOT also for studying phenomena that require particle following in a truly three-dimensional geometry.

Particle simulation has played an important role for the recent investigations on turbulence transport in magnetically confined plasmas. In this paper, theoretical and numerical properties of a gyrokinetic plasma as well as its relationship with magnetohydrodynamics (MHD) are discussed with the ultimate aim of simulating microturbulence on transport time scale using massively parallel computers.