Comment on 'The band structure and optical properties of sulphur nitride polymer'

Comments are made on the paper by Kamimura et al., see ibid., vol.9, p.291, and vol.9, p.L277 (1976), in which it is proposed that the metallic properties of the polymer polysulphurnitride, (SN)x, are stabilized against a Peierls distortion because two overlapping conduction bands cross the Fermi surface. It is shown that for a one-dimensional metal with two bands crossing the Fermi surface, if the sum of the two Fermi wavevectors equals half a reciprocal lattice vector, then there is a strong tendency toward a Peierls distortion which will double the size of the unit cell. The one-dimensional band structure proposed by Kamimura and co-workers for (SN)x will almost certainly exhibit such an instability.