Ab initio prediction of superdense tetragonal and monoclinic polymorphs of carbon

Abstract

Design and synthesis of three-dimensional denser carbons are one of the hot issues in condensed matter physics because of their fascinating properties. Here we identify by ab initio calculations several tetragonal and monoclinic polymorphs of carbon that adopt the t32, t32*, m32, and m32* structures in P421c, P 43212, P 21/c, and C2 symmetry, respectively. These carbon polymorphs have large 32-atom unit cells in all-sp 3 bonding networks comprising five-and six-membered rings that are dynamically stable as verified by a phonon mode analysis. Electronic band structure calculations show that they are insulators with band gaps in the range of 5.19 ∼ 5.41 eV, close to the calculated band gap of 5.34 eV for diamond. Remarkably, these new carbon phases possess extremely high atom number density exceeding that of diamond. The present results establish a new type of carbon phases and offer insights into their outstanding structural and electronic properties.

Global Search for Crystal Structures of Carbon under High Pressure

“…The volume and enthalpy of these structures are shown in Table 1. Among them, MIN70 100GPa is known as r8 42,45 (#122 in SACADA 4 ), and MIN38 100GPa is known as bc8 8 (#20 in SACADA 4 ), as reported in the literature. To the best of our knowledge, the other structures have not been reported.…”

Diamond-XII: a new type of exotic cubic carbon allotrope

“…13–19 There are large numbers of carbon crystals that have been theoretically predicted in previous literature. 19–29 However, only a few of them have been suggested as the candidates for some of the previously discovered small size experimental carbons. For example, the M-carbon, 17,30 W-carbon, 31 Z-carbon, 32,33 H-carbon and S-carbon 34 proposed for explaining the superhard carbon phase synthesized through cold-compressing graphite; 2 the cubic C20-sc, 35 C21-sc and C22-sc 36 predicted as the candidates of the simple cubic carbon sample shock-synthesized by compression of the mixture of carbon black and tetracyanoethylene; 1 the 3D-C24 37 and C3-205 38 proposed for the cubic carbon phase synthesized by cold compressing graphite; 39 and the cubane, 40 BC8 41 and Bcc-C6 35,42 suggested for superdense carbon.…”

Computational discovery of a new rhombohedral diamond phase

“…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. The body-centered-cubic BC8 carbon, adopted * wjt@aphy.iphy.ac.cn by the high-pressure γ -Si allotrope [36], is suggested to be the high-pressure modification of carbon derived from cubic diamond under a pressure of ∼ 1100 GPa [37][38][39][40].…”