The 4th International Conference on Matter and Radiation at Extremes (ICMRE 2019)

453 / 2019-03-08 17:55:04

New carbon allotropes identified in stochastic group and graph constrained searches by RG2 code

Crystal prediction; Carbon allotropes; Superhard materials; First-principles

Plenary track > High Pressure Physics and Materials Science

RG2 is a high-efficient code, based on Random strategy combined with space Group and Graph theory, to generate crystalline structures with well-defined structural features [PRB, 97, 014104 (2018)]. This poster will show two new successful stories about applying RG2 to search novel carbon allotropes. The first one is about a novel 3D cubic carbon allotrope (I-43d) in sp3 hybridization with large-size (188 atom per cubic cell) and low-energy [112 meV/atom higher than that of cubic diamond]. It is a super-hard insulator with an indirect band gap of 7.25 eV, which is the largest band gap in present carbon family [PRL, 121, 175701 (2018)]. The second one is about the discovery of 33 new 2D carbon allotropes including a novel Stone-Wales graphene with intriguing structure (well-arranged Stone-Wales defects) and remarkable stability exceeding than all the previously proposed 2D carbons. It can be constructed through a 90o bond rotation in a sqrt(8)×sqrt(8) supercell of graphene, which is a “magic size” showing better stability than those based on sqrt(9)×sqrt(9), sqrt(12)×sqrt(12) and sqrt(13)×sqrt(13) supercells. Such a “magic size” can be simply understood through a “energy splitting and inversion” model. The calculated vibrational properties and molecular dynamics of SW-graphene confirm that it is dynamically stable. The electronic structure shows SW-graphene is a semimetal with distorted, strongly anisotropic Dirac cones [PRB, 99, 041405(R), 2019].