The formation of gas nanobubbles through the merging of individual fission products of uranium is an important process for the evolution of nuclear fuels. The theoretical description of this process ...is very difficult because both the dynamics of individual atoms in the lattice and the kinetics of evolution of an ensemble of bubbles should be taken into account within a unified model. Such a model is constructed in this work on the basis of molecular dynamics simulations for xenon bubbles in bcc uranium in the case of the excess of interstitial atoms in the crystal matrix. The analysis is based on the molecular dynamics simulation of the nonequilibrium process of formation of xenon nanobubbles from individual Xe atoms dissolved in the crystal matrix. A relation between the size of bubbles and the number of gas atoms in them, as well as the dependence of the diffusion coefficient of bubbles on their radius and the number of interstitial atoms in the gamma-U matrix, has been analyzed. A kinetic model of evolution of the ensemble of bubbles has been proposed to describe the molecular dynamics results and to extrapolate them to long times.
The properties of a polyethylene matrix in contact with carbon nanoinclusions, such as carbon nanotubes and graphene plates, are studied via the molecular-dynamics method. Ultimate shear stresses for ...the polyethylene/graphene interface are calculated, and the effect of the filler aspect ratio on the nanocomposite elastic modulus is considered.
The experimental data on graphite melting temperature remain poorly determined despite the long history of investigations. The experimental results cover the wide span from 3800 to 5000 K that is an ...essentially larger uncertainty than the errors of individual experiments. In this work, we deploy the molecular dynamics method and expand our previous study of the kinetics of graphite melting comparing different carbon interatomic potentials. Here we consider the melting front propagation rate, the aspects of defect formation and single graphene layer decay. The results obtained allow us also to discuss the aspects of graphite-vapor and possible graphite-carbyne phase transitions at low pressures.
The density functional theory (DFT) is a research tool of the highest importance for electronic structure calculations. It is often the only affordable method for ab initio calculations of complex ...materials. The pseudopotential approach allows reducing the total number of electrons in the model that speeds up calculations. However, there is a lack of pseudopotentials for heavy elements suitable for condensed matter DFT models. In this work, we present a pseudopotential for uranium developed in the Goedecker-Teter-Hutter form. Its accuracy is illustrated using several molecular and solid-state calculations.
In this article we study the process of silicon relaxation after swift heavy ion (SHI) irradiation using first-principles-based electron force field eFF. We show that early stages of so-called ...nonthermal melting take place in the nanometric viscinity of SHI trajectory in both bulk Si and Si nanolayer, but result in structural modifications only for the last one. Our results shed light on recent experimental evidence of significant reduction of threashold for SHI-induced damage creation in nanoporous Si.
An accurate computation of the vibrational properties of a crystal lattice, such as phonon density of states and dispersion curves, is necessary for the description of thermodynamic properties of the ...solid state as well as defect migration rates. In this work, we use a simple embedded atom model classical interatomic potential. The phonon density of states for the α and γ phases of uranium at different temperatures was calculated by three methods: the lattice dynamics approach, the Fourier transformation of the velocity autocorrelation function and the Green's function method for lattice dynamics.
We discuss recent experiments performed with an upgraded version of the main magnetic focus ion source (MaMFIS) at the Joint Institute for Nuclear Research (JINR) in Dubna. The device operates in the ...range of electron beam energies extended up to \(40\) keV. The achieved electron current densities are of the order of \(10\) kA/cm\(^{2}\). This assessment is consistent both with the very short ionization time and with the utmost ionization degree of the produced highly charged ions. Due to its high efficiency, the MaMFIS technology is especially promising for ionization of short-lived radionuclides and heavy elements. A new scheme for charge breeding is proposed.
Metal nanoparticles (NPs) serve as important tools for many modern technologies. However, the proper microscopic models of the interaction between ultrashort laser pulses and metal NPs are currently ...not very well developed in many cases. One part of the problem is the description of the warm dense matter that is formed in NPs after intense irradiation. Another part of the problem is the description of the electromagnetic waves around NPs. Description of wave propagation requires the solution of Maxwell's equations and the finite-difference time-domain (FDTD) method is the classic approach for solving them. There are many commercial and free implementations of FDTD, including the open source software that supports graphics processing unit (GPU) acceleration. In this report we present the results on the FDTD calculations for different cases of the interaction between ultrashort laser pulses and metal nanoparticles. Following our previous results, we analyze the efficiency of the GPU acceleration of the FDTD algorithm.
In this paper, we present our first results in the study of the details of nucleation in the homogeneous carbon gas phase using computer calculations with molecular dynamics methods. Direct and ...controlled molecular-dynamics approaches are used and two reactive potentials (ReaxFF and AIREBO) are compared. The calculations have shown that the nucleation process in the AIREBO model is going more actively than in the ReaxFF one.
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