Density functional theory study of hexagonal carbon phases.

摘要: It is reported frequently that the new carbon phases may be harder than diamond (Wang et al 2004 Proc. Natl Acad. Sci. 101 13699 and Mao 2003 Science 302 425). However, mechanism still unclear. In this paper we systematically investigate structural, electronic, mechanical properties of polytypes using first-principles density functional calculations. The results show bulk modulus shear for hexagonal form approach those diamond, suggesting they might hard low compressibility materials. According to semiempirical method hardness based on Mulliken overlap population, hardnesses forms have been evaluated compared diamond. indicate these are superhard. More importantly, bonds in some specific directions which lead noticeable indentation marks anvils observed experiments.