Figure 15.

Electronic structure of chiral and achiral ($u=1/3$) Se. The band structures are calculated for variation of the chirality by changing the position parameter u. From left to right: (a) $u=1/6$ ($S^2=100$%), (b) $u=0.22$ (optimized) ($S^2=45.2$%), (c) $u=0.23$ (experiment) ($S^2=38.4$%), (d) $u=1/3$ ($S^2=0$), (e) $u=1/2$ ($S^2=100$%). The corresponding chirality measures are given in brackets (compare also Figure 5). Note that the parameters $u=1/3$ ($R\overline{3}m$) and $u=1/2$ ($P{6}_{4}22$) result in different space groups and symmetry. Calculations are for variation of the position parameter at optimized lattice parameters.