Ab initio Computationally Generated Nanoporous Carbon and its Comparison to Experiment
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Ab initio Computationally Generated Nanoporous Carbon and its Comparison to Experiment Cristina Romero1, Ariel A. Valladares1 ([email protected]), R. M. Valladares2, Alexander Valladares2 and Alipio G. Calles2. 1 Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Apartado Postal 70-360, México, D.F. 04510, MÉXICO. 2 Facultad de Ciencias, Universidad Nacional Autónoma de México, Apartado Postal 70-542, México, D.F. 04510, MÉXICO. ABSTRACT Nanoporous carbon is a widely studied material due to its potential applications in hydrogen storage or for filtering undesirable products. Most of the developments have been experimental although some simulation work has been carried out based on the use of graphene sheets and/or carbon chains and classical molecular dynamics. Here we present an application of our recently developed ab initio method [1] for the generation of group IV porous materials. The method consists in constructing a crystalline diamond supercell with 216 atoms of carbon and a density of 3.546 g/cm3, then lengthening the supercell edge to obtain a density of 1.38 g/cm3, yielding a porosity of 61.1 % in order to be able to compare with experimental results reported in the literature [2]. We then subject the resulting supercell to an ab initio molecular dynamics process at 1000 K during 295 steps. The radial distribution functions obtained are compared to experiment to discern coincidences and discrepancies. INTRODUCTION Within the wide variety of structural forms of carbon we find the so-called activated or nanoporous carbon. The importance of studying this kind of materials lies in the fact that they have a number of applications as filters, catalysts, bioreactors, cells, electrodes, surgical implants and more [3] because of their unique properties, their large surface area being one of the most outstanding. The most common way to prepare nanoporous carbon is through the pyrolysis of an appropriate precursor such as polyfurfuryl alcohol, sucrose or polyvynildichloride. The selection of this precursor and the pyrolysis temperatures are the main factors responsible for the microporous structure of these materials [4]. Petkov et al. [2] reported nanoporous structures of carbon obtained from neutron diffraction data and produced by pyrolysis of polyfurfuryl alcohol at three diferent temperatures (400, 800 and 1200 °C). They found that carbons processed at 400 °C have a heavily distorted nonplanar structure while the carbons produced at 800 and 1200 °C are constituted of stacked, more or less curved, graphene sheets. Thus, as technological applications increase day by day the goal of emerging models is to determine as precisely as possible the atomic structures of these carbons [5]. Hence the growth in the generation of new models in the last decades is understandable. Some simulational studies employ Monte Carlo (MC) and Reverse Monte Carlo (RMC) techniques using chains of amorphous polymers [6] and graphene sheets [7]. Other studies use molecular dynamics based on th
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