Ab initio electronic band structure calculations for beryllium chalcogenides

The first principles tight-binding linear muffin-tin orbital method within the local density approximation (LDA) has been used to calculate the ground state properties, structural phase transition and pressure dependence of the band gap of BeS, BeSe and BeTe. We have calculated the energy-volume relations for these compounds in the B3 and B8 phases. The calculated lattice parameters, bulk modulus and the pressure-volume relation were found to be in good agreement with the recent experimental results. We have also calculated the cohesive energy for them and they are consistent with the bulk modulus. The calculated B3 to B8 structural transition pressure for BeS, BeSe and BeTe agree well with the experimental results. Our calculations show that these compounds are indirect band gap (Gamma-X) semiconductors at ambient conditions. The calculated band gap values are found to be underestimated by 20-30% which is due to the usage of LDA. After the structural transition to the B8 phase BeS continues to be indirect band gap semiconductor and ultimately it becomes metallic above 100 GPa. BeSe and BeTe are metallic at B3 to B8 structural transition.