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

Abstract

We have studied the correlation between the elastic properties and the electronic structure of nanolayered ${M}_{2}\mathrm{AlC}\phantom{\rule{0.3em}{0ex}}(M=\mathrm{Ti},\mathrm{Zr},\mathrm{Hf},\mathrm{V},\mathrm{Nb},\mathrm{Ta},\mathrm{Cr},\mathrm{Mo},\mathrm{W})$, 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 $P{6}_{3}∕mmc$, prototype ${\mathrm{Cr}}_{2}\mathrm{AlC}$) can be classified into two groups: weakly coupled $(M=\mathrm{Ti},\mathrm{Zr},\mathrm{Hf})$ and strongly coupled $(M=\mathrm{V},\mathrm{Nb},\mathrm{Ta},\mathrm{Cr},\mathrm{Mo},\mathrm{W})$ nanolaminates [Sun et al., Phys. Rev. B 70, 092102 (2004)]. While large potential-induced differences are observed in the elasticity data for the binary carbides (space group $Fm\overline{3}m$, prototype $\mathrm{NaCl}$), 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 et al., 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.