SEMICONDUCTING CSSNBR3

In view of some issues raised recently about the electronic structure and the nature of electronic conduction in simple cubic CsSnBr3, we have carried out a self-consistent density-functional calculation of the electronic structure of this compound using the linear-muffin-tin-orbital (LMTO) method. While previous (empirical tight-binding and pseudopotential) calculations have found this compound to be either a semimetal or a zero-gap semiconductor, the present charge self-consistent calculation, based on the local-density approximation (LDA) within the density-functional theory, shows that it is a narrow gap semiconductor. Contrary to the previous suggestions, we show that the simple cubic symmetry does not prohibit the appearance of an energy gap. We argue that this LDA gap, obtained with the scalar-relativistic LMTO-ASA (atomic-sphere approximation) method, should decrease due to spin-orbit coupling and an estimate of this is provided. It is also shown that a transition from simple cubic to tetragonal phase should lower the gap, but not significantly. The results of the present calculation are consistent with the experimental data available on this compound.