ELECTRONIC-STRUCTURE AND DYNAMIC PROPERTIES OF SOLID ALKALI CYANIDES

The electronic structure of NaCN and KCN has been investigated by mean s of the periodic Hartree-Fock method. These calculations reveal a hig hly ionic character for both compounds. The analysis of the potential energy surfaces in the body-centered orthorhombic phases of both compo unds indicates that rotation of the anions is severely hindered. Quali tatively different results were found for the high-temperature cubic s tructures. In KCN the small barriers allow almost free rotation of the cyanide anions, although shallow minima for the orientation of the CN - ions along the [111] directions of the crystal are found. For NaCN t he situation is quite different, with the CN- units fixed in a random fashion in any of the equivalent positions with the molecular axis ori ented along the [100] directions of the crystal.