Structural, vibrational, electronic, and elastic properties of 2D alkali carbide as a metallic material

Abstract

We have investigated the structural, vibrational, electronic, and elastic properties of two-dimensional alkali carbide, viz. X2C (X = Li, Na, K, Rb) materials. Using the projector augmented wave (PAW) approach within the generalized gradient approximation, the X2C structure has been carefully explored. The X2C compounds are found to be dynamically and energetically stable, according to phonon dispersion studies. After performing both PBE and HSE06 functionals calculations on all X2C compounds, it was confirmed that they all exhibit a metallic bandgap. For Na2C material, we found the highest work function as 6.09 eV in entire alkali carbide materials series. The largest elastic constants (C2D) for Li2C was found in entire series of X2C compounds, with a value of 29.27 Nm−1 in the armchair direction for both the carriers. In addition to the phonon dispersion analysis, we have evaluated their mechanical stability in terms of elastic properties, and the resulting elastic parameters and polar diagrams of Young's modulus and Poisson's ratio validate their mechanical stability. The good metallicity and hardness of 2D X2C might suggest its potential application as hard conductor.