Gennady B. Sushko

Simulation of ultra-relativistic electrons and positrons channeling in crystals with MBN Explorer

A newly developed code, implemented as a part of the MBN Explorer package (Solov?yov et al., 2012; http://www.mbnexplorer.com/, 2012) 1,2] to simulate trajectories of an ultra-relativistic projectile in a crystalline medium, is presented. The motion of a projectile is treated classically by integrating the relativistic equations of motion with account for the interaction between the projectile and crystal atoms. The probabilistic element is introduced by a random choice of transverse coordinates and velocities of the projectile at the crystal entrance as well as by accounting for the random positions of the atoms due to thermal vibrations. The simulated trajectories are used for numerical analysis of the emitted radiation. Initial approbation and verification of the code have been carried out by simulating the trajectories and calculating the radiation emitted by e = 6.7 GeV and e = 855 MeV electrons and positrons in oriented Si(110) crystal and in amorphous silicon.The calculated spectra are compared with the experimental data and with predictions of the Bethe-Heitler theory for the amorphous environment.

Sub-GeV Electron and Positron Channeling in Straight, Bent and Periodically Bent Silicon Crystals

Preliminary results of numerical simulations of electron and positron channeling and emission spectra are reported for straight, uniformly bent and periodically bent silicon crystal. The projectile trajectories are computed using the newly developed module [1] of the MBN Explorer package [2,3]. The electron and positron channeling along Si(110) and Si(111) crystallographic planes are studied for the projectile energies 195-855 MeV.

Simulations of electron channeling in bent silicon crystal

We report on the results of theoretical simulations of the electron channeling in a bent silicon crystal. The dynamics of ultra-relativistic electrons in the crystal is computed using the newly developed part (1) of the MBN Explorer package (2,3), which simulates classical trajectories of in a crystalline medium by integrating the relativistic equations of motion with account for the interaction between the projectile and crystal atoms. A Monte Carlo approach is employed to sample the incoming electrons and to account for thermal vibrations of the crystal atoms. The electron channeling along Si(110) crystallographic planes are studied for the projectile energies 195-855 MeV and different curvatures of the bent crystal.

Kinetics of liquid-solid phase transition in large nickel clusters

In this paper we have explored computationally the solidification process of large nickel clusters. This process has the characteristic features of the first order phase transition occurring in a finite system. The focus of our research is placed on the elucidation of correlated dynamics of a large ensemble of particles in the course of the nanoscale liquid-solid phase transition through the computation and analysis of the results of molecular dynamics (MD) simulations with the corresponding theoretical model. This problem is of significant interest and importance, because the controlled dynamics of systems on the nanoscale is one of the central topics in the development of modern nanotechnologies. MD simulations in large molecular systems are rather computer power demanding. Therefore, in order to advance with MD simulations we have used modern computational methods based on the graphics processing units (GPU). The advantages of the use of GPUs for MD simulations in comparison with the CPUs are demonstrated and benchmarked. The reported speedup reaches factors greater than 400. This work opens a path towards exploration with the use of MD of a larger number of scientific problems inaccessible earlier with the CPU based computational technology.

Simulation of channeling and radiation of 855 MeV electrons and positrons in a small-amplitude short-period bent crystal

Abstract Channeling and radiation are studied for the relativistic electrons and positrons passing through a Si crystal periodically bent with a small amplitude and a short period. Comprehensive analysis of the channeling process for various bending amplitudes is presented on the grounds of numerical simulations. The features of the channeling are highlighted and elucidated within an analytically developed continuous potential approximation. The radiation spectra are computed and discussed.

Molecular dynamics simulation of nanoindentation of nickel-titanium crystal

We present the results of molecular dynamics simulations of nanoindentation of a bimetallic nickel-titanium crystal in the austenitic (cubic) B2 phase. By considering three different types of indenters, namely of square, conical and spherical shapes, we observe the dependence of deformations of the crystalline structure on the type of the indenter. Various load-displacement curves are observed for different indenter types. We perform the molecular dynamics simulations of a full indentation cycle, which includes the loading and unloading stages. On the basis of such simulations we evaluate mechanical properties of the material, namely we calculate hardness and reduced Youngs modulus. We observe variation of the calculated parameters depending on the indenter type and discuss the origin of occurring discrepancies.