Prediction of two-dimensional Cu2C with polyacetylene-like motifs and Dirac nodal line

The design of novel two-dimensional (2D) materials with unique atomistic configurations and exotic properties are highly desirable for material science. Here, we report the prediction of 2D Cu2C layers featuring unique carbon motifs with Dirac nodal lines through evolutionary algorithm searches in conjunction with first-principles calculations. The global minimum alpha-Cu2C is an exciting new structure featuring one-dimensional (1D) zigzag carbon chains sandwiched by two hexagonal-close-packed copper monolayers, conferring to our predicted ground-state 2D alpha-Cu2C an inverse coordination structure. This polyacetylene-like motif (poly-C-2) is also encountered in gamma-Cu2C. Remarkably, the electronic band structure of alpha and gamma-Cu2C phases containing polyacetylene-like chains display a 1D Dirac nodal line, which is protected by the glide plane symmetry. Fermi velocities (v(f)) as high as 2.45 x 10(5) and 3.85 x 10(5) m/s are calculated for alpha and gamma-Cu2C phases, respectively. This work is an effective effort to design and stabilize the 2D copper carbide layers with exotic structures and nodal lines.