Local atomic structures of single-component metallic glasses

In this study we examine the structural properties of single-component metallic glasses of aluminum. We use a molecular dynamics simulation based on semi-empirical many-body potential, derived from the embedded atom method (EAM). The radial distribution function (RDF), common neighbors analysis method (CNA), coordination number analysis (CN) and Voronoi tessellation are used to characterize the metal’s local structure during the heating and cooling (quenching). The simulation results reveal that the melting temperature depends on the heating rate. In addition, atomic visualization shows that the structure of aluminum after fast quenching is in a glassy state, confirmed quantitatively by the splitting of the second peak of the radial distribution function, and by the appearance of icosahedral clusters observed via CNA technique. On the other hand, the Wendt-Abraham parameters are calculated to determine the glass transition temperature (Tg), which depends strongly on the cooling rate; it increases while the cooling rate increases. On the basis of CN analysis and Voronoi tessellation, we demonstrate that the transition from the Al liquid to glassy state is mainly due to the formation of distorted and perfect icosahedral clusters

Density-Diffusion Relationship in Soda-Lime Phosphosilicate

Bioactive glasses release ions such as sodium when implanted in the human body. However, an excess of the released ions can cause problems related to cytotoxicity. The ion release control is considered one of the primary challenges in developing new bioactive glasses. Here, we use molecular dynamics simulations to investigate the effect of the density on atoms' dynamics in an archetypal phosphosilicate bioactive system. The diffusion coefficient displays three main regimes with increasing density. The mobility of the modifiers is significantly affected by the increase of the density, especially Na, compared to other elements. We use a modified Arrhenian model to access the complex dynamic behavior of 45S5 melts and correlate it to the structural changes by evaluating the network connectivity and pair-excess entropy. Overall, our results present a step toward the rational design of bioactive glasses and a key to controlling the ion release of bioactive glasses.Comment: 7 pages, 6 figures, (Under review

NiAl thin film growth on Ni(001) substrate using molecular dynamics simulations

We have studied thin film growth of NiAl on Nickel (001) substrate using molecular dynamics simulations (MD) based on the Embedded Atom Method (EAM) potential. An incidence energy of 0.06 eV at 800 K, 900 K and 1000 K was considered. After the deposition process, we have obtained a B2-NiAl structure film with different percentages; 32.6% for the temperature 1000 K, 30% for 900 K and 25% for 800 K. Our investigation has prompt us to analyze the crystalline structure. During the evolution of deposited film, we observe the formation of grains with different orientation, as well as the appearance of vacancies in Ni and Al sublattices and antisites

DNA Nucleobase Under Ionizing Radiation: Unexpected Proton Transfer by Thymine Cation in Water Nanodroplets

The effects of ionizing radiation on DNA constituents is a widely studied fundamental process using experimental and computational techniques. In particular radiation effects on nucleobases are usually tackled by mass spectrometry in which the nucleobase is embedded in a water nanodroplet. Here we present a multiscale theoretical study revealing the effects and the dynamics of water droplets towards neutral and ionized thymine. In particular, by using both hybrid quantum mechanics/ molecular mechanics and fully ab initio molecular dynamics we reveal an unexpected proton transfer from thymine cation to a nearby water molecule. This leads to the formation of a neutral radical thymine and a Zundel structure, while the hydrated proton localizes at the interface between the deprotonated thymine and the water droplet. This observation opens entirely novel perspective concerning the reactivity and further fragmentation of ionized nucleobases.</p

DNA Nucleobase under Ionizing Radiation: Unexpected Proton Transfer by Thymine Cation in Water Nanodroplets

International audienc

Computational Insights into the Structure of Barium Titanosilicate Glasses

International audienc

Molecular dynamics simulation of surface morphology during homoepitaxial growth of Copper

In this paper, molecular dynamics (MD) simulation of surface morphology during homoepitaxial growth of Copper was investigated. For this purpose, simulations of Cu deposition on the Cu(111) substrate with an incidence energy of 0.06 eV at 300K were performed using the embedded-atom method (EAM). The grown thin film on Cu(111) reveled a rough surface morphology. During deposition, the important fraction of atoms intended for the upper layers undergone a rising rate of about 40% starting from the 2nd period and continued to increase until 65%, while the lower level reached a permanent rate of only 25% by the 4th period. Otherwise, except at the first layer level, the lower layers are incomplete. This void in the lower layers has favored the growth of the upper layers until a rate of 143% and has accelerated their time appearance. Th incidence energy has favored the filling of lower layers by reducing this surface roughness. However, the temperature effect needs more relaxation time to fill the lower layers