Pressure dependence of the relativistic band edges of trigonal Te and Se

The pressure dependence of the valence- and conduction-band edges of trigonal Te and Se is studied theoretically by a self-consistent relativistic ab initio level calculation. The agreement with the experimental $\overrightarrow{\mathrm{k}}·\overrightarrow{\mathrm{p}}$ models is close for Te at 0 kbar. The differences are associated with the missing mass-velocity term in the $\overrightarrow{\mathrm{k}}·\overrightarrow{\mathrm{p}}$ theory. The double valence-band maximum of Se near point $M$ shifts at ∼35 kbar to the vicinity of point $H$ where it attains the two-ellipsoidal $\to$ dumbbell shape. After ∼35 kbar the valence-band edge of Se behaves qualitatively similarly to that of Te (the double maximum tends to change into a single one). Large anisotropic changes induced by pressure are found, especially in the conduction-band edge of Se.