Compressibility and electronic properties of metal cyanides

The compressibility and electronic properties of metal cyanides are investigated within the density functional theory taking into account the dispersion van der Waals interaction. It was shown that gold cyanide has a low linear compressibility (less than 0.1% at a pressure of 1 GPa) and a high linear modulus ($\sim$1200 GPa) along the –Au–CN–Au–CN– chains. Silver cyanide exhibits negative linear compressibility, which correlates with the compressibility of Ag–N coordination bonds. For sodium cyanide, the linear compressibility along the C–N covalent bonds is greater than for gold and silver cyanides, while the elastic anisotropy is less. Unlike sodium cyanide, for gold and silver cyanides, cation-anionic bonds (Au–N, Au–C and Ag–N, Ag–C) are partially covalent in nature, and the upper valence states correspond mainly to the states of cations. The band gap of gold cyanide is smaller than that of silver and sodium cyanides. The band gap widths of gold and silver cyanides significantly decrease with increasing pressure, which indicates the possibility of metallization at sufficiently high pressures.