Water diffusion in carbon nanotubes for rigid and flexible models

We compared the diffusion of water confined in armchair and zigzag carbon nanotubes for rigid and flexible water models. Using one rigid model, TIP4P/2005, and two flexible models, SPC/Fw and SPC/FH, we found that the number of the number of hydrogen bonds that water forms depends on the structure of the nanotube, directly affecting the diffusion of water. The simulation results reveal that due to the hydrophobic nature of carbon nanotubes and the degrees of freedom imposed by the water force fields, water molecules tend to avoid the surface of the carbon nanotube. This junction of variables plays a central role in the diffusion of water, mainly in narrow and/or deformed nanotubes, governing the mobility of confined water in a non-trivial way, where the greater the degree of freedom of the water force field, the smaller it will be mobility in confinement, as we limit the competition between area/volume, and it no longer plays the unique role in changing water diffusivity.Comment: 28 pages, 6 figure

Dióxido de Carbono: um estudo sobre o modelo de simulação computacional EPM2

Neste trabalho utilizamos o modelo de simulação EPM2 para descrever as interações do CO2 como podemos ver nos artigos de IKUSHIMA; SAITO e ARAI (1992), MURTHY; SINGER e MCDONALD (1981), GEIGER; LADANYI e CHAPIN (1990), MERKER et al. (2010) e ZHANG e DUAN (2005). Nosso objetivo, posteriormente, é investigar o comportamento do CO2 e compreender quais modelos conseguem capturar corretamente as interações do bulk e em condições de extremo confinamento

Transport Properties of Hydrogenated Cubic Boron Nitride Nanofilms with Gold Electrodes from Density Functional Theory

The electrical transport properties of a fourlayered hydrogen-terminated cubic boron nitride sub-nanometer film in contact with gold electrodes are investigated via density functional calculations. The sample exhibits asymmetric metallic surfaces, a fundamental feature that triggers the system to behave like a typical p?n junction diode for voltage bias in the interval ?0.2 ? V ? 0.2, where a rectification ratio up to 62 is verified. Further, in the wider region ?0.3 ? V ? 0.3, negative differential resistance with a peak-to-valley ratio of 10 is observed. The qualitative behavior of the I?V characteristics is described in terms of the hydrogenated cBN film equilibrium electronic structure. Such a film shows metallic surfaces due to surface electronic states at a fraction of eV above and below the Fermi level of the N?H terminated and B?H terminated surfaces, respectively, with a wide bulk-band gap characteristic of BN materials. Such a mechanism is supported by transmission coefficient calculations, with the Landauer?Bu?ttiker formula governing the I?V characteristics