Electronic and structural properties of SnO under pressure -: art. no. 014109

Pressure-induced changes in the electronic and structural properties of tin monoxide are examined by means of ab initio density-functional calculations. Also, the pressure shifts of the A(1g) and E-g zone-center phonon modes are derived. The results are compared to recent experimental high-pressure data as well as to previous calculations for ambient conditions. In agreement with earlier findings we observe that the Sn-5s lone pair is not inert but hybridizes with the O-p states. Differences in that respect between SnO and PbO are shown to be a "relativistic dehybridization effect" caused by the large mass-velocity downshift of the Pb-6s states. SnO is a small-gap (indirect) semiconductor at ambient pressure, but an insulator-metal transition occurs as pressure is applied. The transition is estimated to occur around 5 GPa. The gap depends sensitively on the distance between the layers dE(gap)/d ln(c/a)approximate to 21 eV.