Theoretical Study on the Electronic States of Layered Fluorinated Carbon Materials

我们用第一性原理分子动力学方法对氟化石墨和氟化氮化硼进行了理论研究，阐明了层状石墨及其相关材料的氟化可用于1)通过改变组成来控制带隙的宽禁带半导体的合成方法和2)纳米级磁体的合成方法。本课题的主要成果总结如下：1.本课题的主要成果如下。氟化石墨C_nF是一种层状材料，其结构被认为是具有氟化表面的超薄金刚石膜的堆积。当n=L，2，3时，该材料具有直接带隙，当n超过4时，带隙变为间接带隙。我们提出，该材料可用于制作包括半导体激光器在内的光学器件，并从理论上确定了期望输出波长。我们认为该材料是以自然超晶格的形式合成的，并估算了该二维电子系统中电子和空穴的能级。从理论上预测了(BN)_nF的稳定性和性质。我们提出了一种从纳米级石墨和有限纳米管中获得磁性纳米颗粒的方法。从理论上证明了纳米石墨中磁性的存在，这是几位作者所预期的。此外，通过对锯齿形纳米颗粒进行氢化、氟化和氧取代等化学处理，可以在纳米尺度上对其进行控制。这是对无磁性元素磁性材料合成方法的理论预测。在包括关联效应在内的第一原理电子结构计算方面取得了新的进展。我们提出了Kohn-Sham方程的一个推广。实现了互相关方法的加速。

We theoretically investigated fluorinated graphite and fluorinated boron-nitrides using the first-principles molecular-dynamics method and clarified that the fluorination of layered graphite and related materials can be utilized as 1) a synthesis method of a wide-gap semiconductor whose band gap is controllable by changing composition and 2) a synthesis method of a nanometer-scale magnet. Major results of our project are summarized as follows.1. Fluorinated graphite C_nF is a layered material whose structure is regarded as a stacking of ultra-thin diamond films with fluorinated surfaces. The material has a direct gap when n=l,2,3, while the gap becomes indirect if n exceeds 4. We proposed that the material may be utilized for fabrication of optical devices including semiconductor LASER and determined wavelengths of expected output theoretically. We proposed that the material is synthesized as a natural superlattice and estimated energy levels of electrons and holes in this 2-dimensional electronic system. Stability and characteristics of (BN)_nF are theoretically predicted.2. We proposed a way to obtain magnetic nanographite from nanometer-scale graphite and finite nanotubes. Existence of magnetism in nanographite, which has been expected by several authors, is shown theoretically. Moreover, it is controllable by chemical treatments including hydrogenation, fluorination and oxygen-substitution of zigzag-edged nanographite in nanometer scale. This is a theoretical prediction of synthesis methods of magnetic materials without magnetic elements.3. New developments in the first-principles electronic-structure calculations including correlation effects were achieved. We proposed an extension of the Kohn-Sham equation. Acceleration of the trans-correlated method is realized.