Comparative study of the effect of van der Waals interactions on stacking fault energies in SiC

Van der Waals (vdW) interactions have recently been demonstrated to have a non-negligible effect on the theoretical polytype stability and stacking fault energies of SiC. Calculations with density functional theory have been demonstrated to reproduce polytype stability consistent with experimental results when vdW interactions are considered. The effect of vdW interactions on stacking fault energies in SiC is an important engineering issue; however, it has not been studied in detail. Since previous studies used vdW correction methods that are rather simple and semi-empirical, the application of more sophisticated correction strategies and comparison among several proposed methods is required. In this study, we examined the dependence of polytype stability on the vdW correction method. While most methods could reproduce the polytype stability order, the extensively used DFT-D3 and its variants could not since the computed dependence of vdW interaction energy on hexagonality of SiC was small. Then, we examined the stacking fault energies considering vdW interactions. The vdW interactions were found to have a significant effect on the stacking fault energies only when the insertion of stacking faults changes the local hexagonality. The vdW interactions were found to cause negative energy for double Shockley-type stacking faults (DSSFs) in 4H-SiC. This negative energy is inconsistent with the electric energy model for the spontaneous expansion of DSSFs, which assumes that the stacking fault energy is inherently positive. Our results indicate that previous theoretical models may require being modified.