First principles study of the occurrence of gold in pyrite

The occurrence of gold (Au) in pyrite and its effects on the electronic and structural details were investigated by performing first principles calculations based on density functional theory (DFT). It was found that gold would most likely exist in pyrite by incorporating into interstitial lattice sites and by substituting for S atoms. The calculations of the atomic charge showed that gold was present as Au1+ in pyrite. Covalent Au-S bonds and anti-bonding states of Au-Fe bonds were observed to form in pyrite, and a clear hybridization was observed between the S 3p and Au 5d states. The p-type semiconductivity of pyrite was changed to n-type semiconductivity, and Au impurity energy levels were introduced into the energy band. The substitution of Au for S resulted in spin-polarized pyrite, whereas the incorporation of Au in interstitial lattice sites did not change the low-spin state of the pyrite.