Strain induced modifications in the structural, electronic, and vibrational properties of beryllium chalcogenides

We have studied the strain induced modifications in the structural, electronic, and vibrational properties of beryllium chalcogenide (groups II–VI) BeX (where X = S, Se, and Te) compounds by employing first-principles calculation within the framework of density-functional theory based on the plane-wave pseudopotential method with implementation of the local-density approximation functional. We have gradually applied biaxial strain on BeX compounds and observed changes in the structure of these compounds. The calculated structural properties such as lattice parameter, bulk modulus, and bandgap are in good agreement with the previously reported theoretical and experimental values. It is found that the calculated bandgaps are indirect from the Γ → X direction and vary with the applied strain. It is also confirmed by the density of states calculations. To study the dynamical stability of BeX compounds, we have calculated the vibrational properties. The calculated bandgap and phonon frequencies vary with the applied strain. For a higher value of the applied strain, we found imaginary phonon frequencies for all three compounds. The bandgap and phonon frequencies decrease as we move from a lower to a higher atomic number (i.e., from S to Te) for BeX compounds.