Energetics and Structural Investigation of Double-Walled Carbon and Silicon Nanotubes
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Energetics and Structural Investigation of Double-Walled Carbon and Silicon Nanotubes Solange B. Fagan1, Daniela S. Sartor1, R. Mota1, R. J. Baierle2, Antônio J. R. da Silva3 and A. Fazzio1,3 1 Departamento de Física, Universidade Federal de Santa Maria, 97105-900, Santa Maria, RS, Brazil. 2 Departamento de Ciências Exatas, Centro Universitário Franciscano, 97010-032, Santa Maria, RS, Brazil. 3 Instituto de Física, Universidade de São Paulo, CxP 66318, 05315-970, São Paulo, SP, Brazil. ABSTRACT Using two different approaches: Monte Carlo simulations with Tersoff empirical potential and first principles calculations, the energetics and the structural properties of double-walled carbon and silicon nanotubes are investigated. Through Tersoff potential, the changes on cohesive energies for the Si and C systems are determined for several outer tubules for a fixed inner tube. Adopting first principles calculations, based on density functional theory, the trends, in terms of the cohesive energies, are compared with the corresponding obtained results using Tersoff empirical potential. The structures, specially of the most stable double-walled nanotubes, are discussed. INTRODUCTION While experimental observations have involved abundant specimens of two or more concentric tubes, theoretical studies have been devoted mainly to single-walled nanotubes (SWNT). The reason has been essentially because multiwalled nanotubes (MWNT) are assumed to be much more complex than the SWNT. Since the first works [1], it was clear that the understanding of the properties of MWNT, in particular concerning the interlayer coupling, was not a simple task. In fact, it is possible to affirm that in the field of electronic and structural properties of the MWNT a lot remains to be done, and it has been one of the topics of primary interest [2]. About the electronic properties, Saito et al. [3] calculated the band structure using the tight-binding method, and showed that the individual nanotubes retained their respective character (metallic or semiconducting) when the interlayer interactions were included. Differently, Charlier et al. [4] considered the case of a metallic tube inside another metallic one, and found that in certain configurations the interlayer interactions can cause both tubes to become insulating. These and other results [5] make it clear that much more work is required to determine the structural and electronic properties of MWNT. The aim of this paper is to investigate the structural influence of a second tubule around a first one. When studying the hypothetical Si double-walled nanotubes (DWNT), we take as our starting geometries structures that are analogous to the C DWNT, as done previously [6-8] for SWNT. It is worth continuing the comparison between the C and Si beyond the study of SWNT nanotubes [6,7] for at least two reasons: i) it is always interesting, from a basic point of view, to compare the properties of elements like Si and C that belong to the same column in the periodic table, and ii) even more interesting, as the s
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