非晶态碳的结构：碳链的存在

Structure of Amorphous Carbon:Existence of Chain Sites

对非晶碳的结构在某此低密度下是否有二度配位（ｓｐ．链状结构）的存在目前仍然存在争议，在用两种都相当精确的理论方法（Ｃａｒ－Ｐａｒｒｉｎｅｌｌｏ和紧束缚的分子动力学方法）研究密度约为２ｇ／ｃｍ￣３的非晶碳结构时，对是否有碳链的存在给出完全不同的结论，本文利用第一原理的自治赝势平面波方法，计算了一维ｓｐ碳链，二维ｓＰ￣２石墨和三维ｓｐ￣３金刚石结构的结合能、键长等性质随平面波数目的变化，澄清了两个理论结果的矛盾，支持了非晶碳在密度约为２ｇ／ｃｍ￣３时应有碳链存在的结论．

The ration of threehold sp￣2 to fourfold sp￣3sites and the existence of sp carbonchain in a-Cat some lower density are still subject to controversy. Two well-established theoreti-cal calculations(with Car-Parrinello and Tight-binding molecular dynamics methods)give differ-ent conclusions concerning the existence of carbpon chain in a-C for density around 2 g/cm￣3.Inorder to resolve the controversies between two theories,we ernploy the norm-conserving non-lo-cal pseudopotential plane wave method to study the cohexive energies and bond lengths of 1-D spcarbon chain,2-D sp￣2 graphite and 3-S sp￣3 diamond structures as a function of the plane wavenumbers in the basis set.Our calculations support the result that sp chain sites should exist in theamorphous carbon for density around 2 g/cm￣3