Estudo teórico de nanotubos singlewalls e Doublewalls de carbeto de silício

Abstract

The study of nanoscale structures has contributed to new discoveries and advances in nanotechnology. The application and understanding of physical and chemical properties of these new materials has stimulated interest in the areas of science such as Chemistry, Physics and Engineering. In 1991 cylindrical structures formed by coaxial tubes, called multiwall nanotubes, were discovered by Iijima and colleagues since then, has driven the search for synthesis and theoretical study of these nanostructures. This work presents a theoretical study with silicon carbide nanotubes formed only by one nanotube, known as singlewalls nanotubes and by two coaxial tubes, known as doublewalls nanotubes being performed quantum-mechanical calculations using the semi-empirical methods AM1 and MNDO and ab initio HF and B3LYP with 3-21G and 6-31G basis functions. Dozens of algorithms were developed in linux shell to obtain the models, assistance in process optimization, data collection and filtering of results. To calculate energy were selected one hundred models singlewalls, being fifty in armchair conformation and fifty zigzag conformation and twenty models doublewalls armchair and zigzag. The analysis of results for models singlewalls showed that the first calculations showed more stable regions alternating with release of distances and angles between the constituint atoms, however, indicating more stable regions that were found after repeated energy calculations. Analysis of mean distances binding showed values around the center of singlewalls about 1.70 angstroms and showed variations at the ends was observed where the closure at one end and open at the other for the zigzag model, however for opening armchair was at both ends. Analysis of variance showed that energy decreased in value with increasing height and diameter. Comparing singlewalls armchair and zigzag, the armchair were more stable. Analyzes of |HOMO-LUMO| showed variations with the mean tending to regions between insulating and semiconductors materials. The collection of point charges showed larger fluctuations in the extremities and greater symmetry for models armchair. The results of the analyzes of variance of energy doublewalls were similar to singlewalls where there was a decrease in the amount of variations with increasing height and diameter. In the analysis of stability between singlewalls and doublewalls showed that there was variation between both structures with values tending to zero, indicating the possibility of synthesizing both.