三维碳烯和碳炔晶体结构的第一性原理理论模拟计算研究

A wide range of properties of carbon materials is determined by the possibility of the existence of carbon atoms with four basic types of single, double, triple, and aromatic carbon-carbon bonds, which are closely related to the bonding configurations in ethane, ethene, ethyne, and benzene-type hydrocarbon structures. At ambient conditions, graphite is the thermodynamically most stable carbon configuration with two-dimensional (2D) benzenoid sp2 bonding network. Diamond, is the second most stable allotrope of carbon with all sp3 bonding state, forming a very rigid three-dimensional (3D) carbon network. Linear carbyne, which is related to polyyne-like unsaturated hydrocarbon with alternating single and triple carbon-carbon bonds, forms the simplest one-dimensional (1D) carbon chain. Under high compression graphite can transform to diamond or diamond-like sp3 carbon forms. Meanwhile, since the discovery of fullerenes, nanotubes, and graphene, considerable theoretical and experimental efforts have been made to search and assess new potential carbon allotropes. Intriguing among them are the so-called graphyne and graphdiyne, which are constructed by replacing one-third of the C-C bonds in graphene sheet with acetylenic (-C≡C-) or diacetylenic (-C≡C-C≡C-) linkages. Thus far, large-scale graphyne and graphdiyne films composed of sp+sp2 hybrid network have been successfully synthesized under laboratory conditions. However, the related 3D structures in all-sp2 bonding networks remain largely unexplored. Recently we identified by ab initio calculations a new type of 3D chiral framework structures of cR6, cT8 and rh6 carbene in all-sp2 bonding networks based on ethene-type planar pi-conjugation. These structures are found energetically more favorable than previously proposed carbene structures such as K4, H6 with twisted pi-bonds, and the new rh6 carbon has been confirmed experimentally in the morphed graphene nanostructures. These findings suggest a new approach to constructing covalent network structures. ..In present work, we perform by ab initio calculations a detailed study on the 3D carbene and carbyne structures: (1) we identify the possible crystalline structures of carbene and carbyne consisting of polyyne-like carbon chains or polycyclic aromatic hydrocarbons; (2) we study the possible pathway, structural stability and phase transformation under pressure; (3) we study the x-ray diffraction (XRD) patterns and Raman spectrum compared to the experimental data to understand the unconfirmed new carbon phases in recent experiments. The present study should establish new carbon phase and offer insights into its outstanding structural and electronic properties.

碳是自然界中最为广泛分布和存在的元素之一。其特有的碳碳单键、双键、三键以及苯基大π键赋予了碳元素结构的多样性和丰富的物理性质。随着人们对两维石墨烯、石墨炔以及三维金刚石结构的深入研究，三维碳烯和碳炔的研究已提到了日程。最近通过第一性原理模拟计算，我们较系统地研究了一维碳炔链在不同的折叠方式下形成三维碳烯晶体的机制，提出了一个新的由六折螺旋碳链构成的rh6碳烯晶体结构并被实验所验证。本项目拟在我们已有工作的基础上，深入探讨不同形态不同尺寸的碳原子链以及多环芳烃分子碎片通过乙烯型(>C=C<)碳碳双键结合构成碳烯和碳炔晶体结构的规律；通过第一性原理动力学模拟计算，从热力学和动力学两方面系统地研究三维碳烯和碳炔晶体的形成机制、结构稳定性与高压相变；通过和以往实验数据的比对分析，解释实验现象，提出新的碳结构，为实验提供理论支持与帮助。

碳是自然界中最为广泛分布和存在的元素之一，其特有的碳碳单键、双键、三键以及苯基大π键赋予了碳元素结构的多样性和丰富的物理性质。通过第一性原理计算，我们在碳烯和碳炔晶体结构的结构稳定性和物性研究方面取得了一系列重要进展:（1）发现具有all-sp2键的三维六角石墨烯碳结构tr32、tr50、tr98、以及由sp2-sp3杂化键构成的正交三维碳烯so-C12、oC24、oP16呈现nodal line拓扑半金属特性，进而发现具有sp2-sp3杂化键的体心正方bct-C40碳结构呈现一种新的nodal-net半金属特性;（2）将乙炔和丁二乙炔键插入到体心立方C8晶格中构建了两个新型具有sp1-sp3键三维碳炔结构。能带计算表明这些新的碳素异构体是半导体；（3）发现了多个由sp3键构成的超硬碳结构BC14、SC48、R16、O16、O32, 并解释了有关未确定的实验XRD结构；（4）通过三折形变（three-fold distortion）重构机制，由(6,0)和(9,0)碳纳米管得到了两个稳定的具有sp2-sp3杂化键和P63/mcm对称性的(6,0)-hp24和(9,0)-hp36三维碳结构，它们在拓扑学上分别对应于二维石墨烯和石墨炔，具有半导体特性。在此项目的支持下，共发表论文15篇，其中PRL 1篇， J. Phys. Chem. Lett. 1篇，Carbon 1篇，PRB 4篇，PCCP 3篇，JCP 1篇。这些研究增进了我们对碳及有关实验现象和物性的认识和理解。