A THEORETICAL-STUDY OF PRESSURE EFFECTS ON SELENIUM-I

Total energy calculations have been carried out on the hexagonal phase of selenium in order to study the effects of pressure on the internal structure, electronic band structure and the Gamma-point vibrational modes. The Kohn-Sham equations are solved within the local density approximation using the pseudopotential method with a plane wave basis set. The structure is obtained at several pressures by optimising the size of the unit cell and allowing the atoms to move under the influence of the Hellmann-Feynman forces. It is found that the band gap closes quickly with pressure and, while constraining the space group, we observe a band closure at the H point at a pressure of 20 GPa. We further show that the valence bands split into separate groups which can be associated with covalent bonds, lone pair p-like orbitals and s-type atomic orbitals.