Coupling in nanolaminated ternary carbides studied by theoretical means: The influence of electronic potential approximations

We have studied the correlation between the elastic properties and the electronic structure of nanolayered M2AlC (M=Ti,Zr,Hf,V,Nb,Ta,Cr,Mo,W), by ab initio calculations using two versions of projector augmented wave (PAW) potentials and full-potential, all-electron approach. It was reported that these ternary carbides (space group P6(3)/mmc, prototype Cr2AlC) can be classified into two groups: weakly coupled (M=Ti,Zr,Hf) and strongly coupled (M=V,Nb,Ta,Cr,Mo,W) nanolaminates [Sun , Phys. Rev. B 70, 092102 (2004)]. While large potential-induced differences are observed in the elasticity data for the binary carbides (space group Fm (3) over barm, prototype NaCl), the elasticity data for the ternary carbides are clearly not affected by the choice of PAW potentials. The partial density of states data discussed here unambiguously show that the physical explanation of the classification notion put forward previously [Sun , Phys. Rev. B 70, 092102 (2004)] is not influenced by the calculation method selected. However, these results raise questions with respect to the quality of the electronic approximation, in particular for the description of the binary transition metal carbides by PAW potentials.