致密碳化锂中碳的聚合形式
Polymeric forms of carbon in dense lithium carbide
摘要：
对碳纳米材料的巨大兴趣继续刺激旨在实现碳纳米线的密集研究活动，因为预期碳原子的线性链将显示新颖的和技术相关的光学、电学和机械特性。尽管碳的各种同素异形体（例如，金刚石、纳米管、石墨烯等）是最为人所知的材料之一，但由于难以使碳的悬挂键适当饱和，因此稳定一维形式的碳仍然具有挑战性。在这里，我们通过第一性原理计算表明，有序的聚合物碳链可以稳定在固体锂$_2$ C $_2$在中等压力下。这种压力诱导相（5 GPa以上）由嵌入锂笼中的双重锯齿形碳链的平行阵列组成，由于在\emph{sp} $^2$样杂化物中形成部分占据的碳孤对态，其显示出金属特征。发现在较宽的压力范围内，该相仍然是最有利的相。在极压（大于215 GPa）的结构和电子相变向绝缘单键三重协调的碳网络的预测。
英文摘要：
The immense interest in carbon nanomaterials continues to stimulate intense research activities aimed to realize carbon nanowires, since linear chains of carbon atoms are expected to display novel and technologically relevant optical, electrical and mechanical properties. Although various allotropes of carbon (e.g., diamond, nanotubes, graphene, etc.) are among the best known materials, it remains challenging to stabilize carbon in the one-dimensional form because of the difficulty to suitably saturate the dangling bonds of carbon. Here, we show through first-principles calculations that ordered polymeric carbon chains can be stabilized in solid Li$_2$C$_2$ under moderate pressure. This pressure-induced phase (above 5 GPa) consists of parallel arrays of twofold zigzag carbon chains embedded in lithium cages, which display a metallic character due to the formation of partially occupied carbon lone-pair states in \emph{sp}$^2$-like hybrids. It is found that this phase remains the most favorable one in a wide range of pressure. At extreme pressure (larger the 215 GPa) a structural and electronic phase transition towards an insulating single-bonded threefold-coordinated carbon network is predicted.
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