Narrow Results

The electronic, elastic, acoustic and optical properties of fluorite phase TiO₂ are calculated by using the first principles method. Different exchange-correlation functionals are used with the ultrasoft plane wave pseudopotential method under pressure from 0 GPa to 90 GPa. The calculated values of the lattice constant, cell volume, bandgap, bulk modulus and the pressure derivative of bulk modulus are in agreement with the prior published results. The calculated elastic parameters show that the fluorite structure is mechanically stable, the ratio of bulk to shear modulus indicates that it is brittle, and pressure derivative of the bulk modulus shows that it is not a super hard material, but a hard material. The longitudinal and transverse acoustic velocities in the direction [100], [110] and [111] are computed by using prior determined data. Besides, the optical properties are also studied under the aforementioned range of pressure, and the results show more photolytic activity over the other phases.

Using the ab initio plane-wave ultrasoft pseudopotential method based on the generalized gradient approximation (GGA), we investigate the bandgap tuning in monolayer phosphorene in terms of applying external electric fields perpendicular to the layers. The bandgap continuously decreases with the applied electric fields, eventually rendering them metallic. The phenomenon is explained by the giant stark effect. The interlayer P-P distance also result in the semiconductor-to-metal transition. The phosphorene exhibits the significant bandgap tuning ability under different strains with 5% variation. Our investigations show the bandgap change for the fabrication of novel electronic and photonic devices.