Predicted two-dimensional electrides: Lithium–carbon monolayer sheet

Electrides have attracted great attention since they not only show the fascinating chemical properties but also are of fundamental importance for science and technology application. Here we have systematically explored the two-dimensional (2D) structures of Li–C system with different stoichiometric (LixC, x=1/3,1/2,1,2,and3) monolayer sheets using unbiased swarm structure search. Interestingly, the predicted 2D structures of LiC2 and LiC3 monolayers are metallic, which can be viewed as lithium doped graphene structures. For the two LiC monolayers (LiC-I and LiC-II), the calculations exhibit they are insulators with very large band gaps of 3.98 eV and 3.46 eV, respectively. Li2C monolayer is found to be a semiconductor with a narrow band gap of 0.21 eV, while Li3C is a metal. In Li-rich Li2C and Li3C monolayers, C atoms exit as the C-pairs in the center of the Li six-membered rings. More interestingly, the electron localization function suggests the Li–C system is likely to become 2D electride compounds. The present results open an avenue to design and understand electride compounds in 2D materials.