Developing theoretical and computational methods to study nanocarbon systems with large unit cell

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Fullerenes, nanotubes, and other nanocarbon materials are the key materials in nanoscience and nanotechnology. They show structure-dependent mechanical and electronic properties. On the other hand, such rich structural possibilities make it difficult to predict the properties of large unit-cell systems. In some cases, the unit cell contains more than a thousand atoms. In this sense, one usually needs to use several kinds of theoretical methods depending not only on the purpose of the research but also strongly on the system size. Usually one has to set up different input files for each computational program system. Especially in the case of first-principles methods, there are a lot of element-dependent parameters one has to set up. However, if one deals with only carbon, most of the input parameters can be fixed, and essentially the input file contains only the atomic geometry. In this project we have developed a combined system for nanocarbon materials which can utilize model-potential method, tight-binding method, molecular-dynamics method, and the first-principles methods based on the density-functional theory. One only has to prepare the atomic-geometry file independent of the method to be used. This dramatically simplifies the process for studying theoretically the nanocarbon systems.