Despite of the numerous theoretical and experimental investigations on the mechanical properties of graphene as a unique nano-structured material, a precious value for this important property has not yet been presente...
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Despite of the numerous theoretical and experimental investigations on the mechanical properties of graphene as a unique nano-structured material, a precious value for this important property has not yet been presented. In the present work, the Young's modulus of single layer graphene sheet has been investigated by using comprehensive classic as well as quantum mechanics (QM) calculations. Molecular mechanics (MM) approach with various well-defined force-fields such as AIREBO, Tresoff and EDIP potentials have been considered. In QM category, several conventional methods (DFTB and DFT-LDA/GGA) have been employed. The results show that EDIP potential method predicts more accurately the graphene Young's modulus value compared to experimental results. Furthermore, despite the various theoretical results reported elsewhere, the EDIP potential calculations result reveals that Young's modulus has the same value at both zigzag and armchair directions. From the results obtained here, we found that among the various MM and QM methods considered here the EDIP method seems to be the most convenient method for evaluation of both structural geometries and mechanical properties of carbon based graphene-like materials. This is because of its less computational costs accompanied with reliable results comparable with the experiments. (C) 2015 Elsevier Ltd. All rights reserved.
Amorphous calcium carbonate (ACC), as observed by diffraction or infra-red spectroscopy, is especially significant as a precursor in biomineralization. The atomic structure and mechanisms for transformation to the cry...
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Amorphous calcium carbonate (ACC), as observed by diffraction or infra-red spectroscopy, is especially significant as a precursor in biomineralization. The atomic structure and mechanisms for transformation to the crystalline phases are still unknown. It is conceivable that insertion of water molecules could give rise to distortions that result in the observed diffraction patterns and infrared spectra. We use the VASP density functional theory code to relax model supercells with 24 formula units of CaCO3 where we have inserted up to 5 water molecules, corresponding to 3.75 wa. The main effect is tilting of the carbonate planes, which can be as high as 50 degrees. This leads to a range of Ca-O distances that are consistent with the observed changes in the IR spectra in ACC. The spread in cation-cation distances is not enough to destroy coherent diffraction from regions 70 nm across, and so does not explain amorphous diffraction profiles. (C) 2015 Elsevier B.V. All rights reserved.
We present a renormalization approach to solve the Sznajd opinion formation model on complex networks. For the case of two opinions, we present an expression of the probability of reaching consensus for a given opinio...
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We present a renormalization approach to solve the Sznajd opinion formation model on complex networks. For the case of two opinions, we present an expression of the probability of reaching consensus for a given opinion as a function of the initial fraction of agents with that opinion. The calculations reproduce the sharp transition of the model on a fixed network, as well as the recently observed smooth function for the model when simulated on a growing complex networks.
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