Dinâmica molecular e cálculos ab initio em moléculas, nanocones de carbono e agregados de água

Abstract

This work is within the scope of Nanoscience and Nanotechnology, whose main objects of study are systems (nanostructures, nanoparticles, nanoclusters, etc.) with characteristic dimensions in the range 1–100 nm (1 nm = 10 ˚A). The following systems were investigated: (a) molecular carbon nanobaskets, their structural properties and their interaction with the L-alanine amino acid; (b) nested carbon nanocones and their interaction; (c) water aggregates and their structural transition depending on the temperature. These nanosystems were explored using tools of classical molecular dynamics, which allows for simulations involving thousands or even millions of atoms, and density functional theory, which allows for the electronic ground state calculations of systems with hundreds of atoms. With the study of the carbon nanobaskets corannulene – C20H10, hemifullerene – C30H12, acenaphthoindacenopicene – C32H12 and Circumtrindene – C36H12, it was obtained that they are stable at high temperatures, and that their capacity to trap the amino acid L-alanine is dependent on the level of π- σ orbitals mixing which, on the other hand, is related to curvature. Carbon nanocones are conical nanostructures observed during the synthesis process of carbon nanotubes, existing with tip aperture angles of 19.2◦, 38.9◦, 60.0◦, 83.6◦, and 112.9◦. Experimentally, carbon nanocones exhibit nesting, i.e. they are stacked along a common axis. Interaction potentials of pairs of nested carbon nanocones were calculated here, and it was shown that they depend on the tip aperture angles and on the number of carbon atoms. Finally, the interaction between water molecules through hydrogen bonds gives rise to stable clusters of water: dimers, trimers, tetramers, pentamers, hexamers, etc. which are formed by two, three, four, five, six, etc. water molecules, respectively. The potential energy of interaction between layered clusters was calculated, and it was demonstrated a surprisingly transition from two adjacent layers of water trimers to one layer with a water hexamer, from four adjacent layers of water trimers to one layer with two water hexamers, an also from three layers of water tetramers to one layer with two water hexamers. All research results presented here are a small part of the Instituto de NanoBioEstruturas & Simula¸c˜ao NanoBioMolecular [NANO(BIO)SIMES] activities, one of the Institutos Nacionais de Ciência e Tecnologia funded by CNPq beginning in 2009, whose aim is to develop scientific research and to promote the formation of high-level personnel in the field of nanobiostructure and nanobiomolecular simulations.