Structural transition of FeSe under high pressure

The density functional calculations of the energy band structure and density of state for the tetragonal PbO-type phase \alpha-FeSe and hexagonal NiAs-type phase \beta-FeSe are reported in this paper. The structural phase transition from tetragonal to hexagonal FeSe under high pressure is investigated, it is found that the calculated transition pressure for the \alpha → \beta phase transformation is 8.5 GPa. Some fluctuations in the transition pressure maybe occurred by different external factors such as temperature and stress condition. There is about 17% volume collapse accompanying the \alpha → \beta phase transformation.