Electronic structure of CuCl

Self‐consistent energy band structure obtained by two different ab initio methods (LCAO and LMTO) shows that CuCl is a direct gap semiconductor. No indirect gap is found at ambient or high pressures as required by Rusakov's model and Abrikosov's speculations invoking Herring's “excitonium” state as the origin of superdiamagnetism or high‐temperature superconductivity in CuCl. Band gap predictions are compared with several existing experiments including new infrared absorption measurements we have performed and report here.