Possibility of imperfections in α-boron

Recently, we have shown by density functional theory calculations that alpha-boron is the most stable phase at low temperature among icosahedron-based boron crystals. This is consistent with low-temperature crystal growth of alpha-boron. A problem of the calculation is, however, that the conclusion would be changed if defect states for beta-boron, which are observed in experiment, were taken into account. This urges us to suspect the perfectness of alpha-boron crystal. In this paper, we investigate possibility of imperfections of alpha-boron from the standpoint of crystal stability. Intrinsic defects of vacancy and self-interstitial have been examined. Based on the total energy calculations, we conclude that intrinsic defects are not present at a level above 0.1 at%.