Computational prediction of body-centered cubic carbon in an all-sp3six-member ring configuration

Abstract

Recent shock compression experiments produced clear evidence of a new carbon phase, but a full structural identification has remained elusive. Here we establish by ab initio calculations a bodycentered cubic carbon phase in Ia3d (O 10 h ) symmetry, which contains twelve atoms in its primitive cell, thus termed BC12, and comprises all-sp 3 six-membered rings. This structural configuration places BC12 carbon in the same bonding type as cubic diamond, and its stability is verified by phonon mode analysis. Simulated x-ray diffraction patterns provide an excellent match to the previously unexplained distinct diffraction peak found in shock compression experiments. Electronic band and density of states calculations reveal that BC12 is a semiconductor with a direct band gap of ∼ 2.97 eV. These results provide a solid foundation for further exploration of this new carbon allotrope.

Computational discovery of a new rhombohedral diamond phase

“…However, in contrast to the uniform bond length of 1.544 Å in diamond, R16 carbon contains four distinct bond lengths, 1.457, 1.488, 1.569, and 1.748 Å, and it also has varying bond angles ranging from 100.13 • to 120.68 • . These structural arrangements are different from those in BC8 carbon that contain two distinct bond angles of 101.22 • and 116.31 • and two distinct bond lengths of 1.446 and 1.611 Å [32]. Note that although R16 and BC8 have similar crystalline structures, they hardly convert to each other due to the relatively large kinetic barrier; meanwhile, our kinetic calculations show that R16 carbon can be easily transformed from supercubane [see Figs.…”

“…In addition, cubic modifications of carbon have been produced during the heating of carbon soot or shock compression of polycrystalline graphite [28][29][30], which led to a proposed simple cubic carbon phase termed SC24 in P a3 symmetry [31]. Very recently, a new cubic modification of carbon denoted as BC12 in I a3d symmetry [32] is proposed to be a likely candidate structure found in the shock-compressed tetracyanoethylene powder [29]. Moreover, carbon crystals share many of the structures adopted by silicon and germanium [33][34][35], including the denser R8, BT8, BC8, and ST12 carbon.…”

Stochastic generation of complex crystal structures combining group and graph theory with application to carbon

“…The literature records that various cubic carbons 21,72-77 can be synthesized under high pressure conditions and some of them are still structurally unresolved. Much theoretical effort has been expended on predicting cubic carbon crystals over the past decades [56][57][58][78][79][80] . According to SACADA (New update from 2 May 2017), there about 38 sp 3 carbons belonging to the cubic system, including diamond, BC8 47,81 , T-carbon 29 , fcc-C34 82 and sc-C46 82 .…”

“…Over recent decades, many interesting aspects of elemental carbon have been explored. For example, much theoretical effort has been expended on the enumeration of hypothetical metastable carbon structures [24][25][26][27][28][29][30][31][32][33][34][35] , predicting potential superhard carbon materials [36][37][38][39][40][41][42][43][44][45] , searching for possible super-dense carbon crystals [46][47][48] , solving the crystalline structures of the previously synthesized carbon phases [49][50][51][52][53][54][55][56][57][58][59] , determining the ultimate fate of carbon under extreme compression 60 , as well as designing direct-band gap carbons for solar cell application 61,62 . As documented in the Samara Carbon Allotrope Database (SACADA: http://sacada.sctms.ru/ (accessed December 24, 2016).…”

Modeling of synthesis pathways for diamond-like polycyclobutane phases

“…Currently, more than a hundred of such phases are predicted that can be obtained from various graphite-like precursors [5, 8 -10]. Among these diamond-like phases, the most interesting for researchers are the superhard phases LA3 (polycyclobutane) and LA5 (Y-carbon), crystal structures of which are formed by polymerized cyclobutane rings [5,8,[11][12][13][14]. However, to date, detailed studies of possible methods for obtaining the structures of phases LA3 and LA5 have not been carried out.…”