arXiv subjects

A. Proykova

Publications and source records attributed to A. Proykova.

4 recordsLinked to original sources

arXiv2008

Useful vacancies in Single Wall Carbon Nanotubes

The electronic and structural properties of zigzag and armchair single-wall carbon nanotubes (SWCNT) with a single vacancy or two vacancies located at various distances have been obtained within the frame of the Density Function Theory (DFT) and a Molecular Dynamics method. It is found that the vacancy defects interact at long ranges in armchair SWCNTs unlike the short-range interaction in zigzag SWCNTs. The density of states for different vacancy densities shows that the local energy gap shrinks with the vacancy density increase. This and other results of the investigation provide insight into understanding the relation between the local deformation of a defective nanotube and its measurable electronic properties.

physics.atm-clus↗

arXiv2002

Optimization of molecular clusters configurations using a Genetic Algorithm

We present a genetic algorithm developed (GA) to optimize molecular AF_6 cluster configurations with respect to their energy. The method is based on the Darvin's evolutionary theory: structures with lowest energies survive in a system of fixed number of clusters. Two existing structures from a given population are combined in a special way to produce a new structure (child) which is kept if its energy is lower than the highest energy in the ensemble. To keep the population constant we reject the structure with the highest energy. This algorithm gives a better result than the optimization techniques used previously. Using the GA we have found a new structure corresponding to the (seemingly) global minimum. The most important result is that the new structure is detected only if the molecular cluster contains more than a critical number of molecules.

physics.atm-clus↗

arXiv2002

Charge Dependence of Temperature-Driven Phase Transitions of Molecular Nanoclusters: Molecular Dynamics Simulation

Phase transitions (liquid-solid, solid-solid) triggered by temperature changes are studied in free nanosized clusters of TeF_6 (SF_6) with different negative charges assigned to the fluorine atoms. Molecular dynamics simulations at constant energy show that the charge increase from q_F=0.1 e to q_F=0.25 e shifts the melting temperature towards higher values and some of the metastable solid states disappear. The increased repulsive interaction maintains the order in molecular systems at higher temperatures.

physics.atm-clus↗

arXiv2002

Parallel J-W Monte Carlo Simulations of Thermal Phase Changes in Finite-size Systems

The thermodynamic properties of 59 TeF6 clusters that undergo temperature-driven phase transitions have been calculated with a canonical J-walking Monte Carlo technique. A parallel code for simulations has been developed and optimized on SUN3500 and CRAY-T3E computers. The Lindemann criterion shows that the clusters transform from liquid to solid and then from one solid structure to another in the temperature region 60-130 K.

physics.comp-ph↗