First-principles study of the optical properties of PbTiO

The optical properties of PbTiO3 were studied from first principles using the density functional theory. The dielectric functions and optical constants are calculated using the full potential–linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA). The theoretical calculated optical properties and energy loss (EEL) spectrum yield a static refractive index of 2.83 and a plasmon energy of 23.1 eV for cubic phase. The effective electron number at low energy saturates near 20 eV with the value of 18.1 for the effective electron number. In the tetragonal phase the static refractive index decreases to 2.59 and yields a plasmon energy of 22.7 eV

Study of the stability and interwall distance of (6,0)@(n,0) double-walled silicon carbide nanotubes by the vdW-DFT method

In this work, the stability and electronic structure of zigzag double-walled silicon carbide nanotubes (DWSiCNTs) (6,0)@(n,0) (with n=11-17) were investigated by using ab initio Van der Waals density functional. By calculating the formation energy and the binding energy of each double walled nanotube, the best interwall distance for the outer nanotube was indicated. The results revealed that (13,0) nanotube could be the best external nanotube for the (6,0) internal nanotube with 3.53 Åinterwall distance to make (6,0)@(13,0) DWSiCNT. The structural calculations also revealed that all studied silicon carbide nanotubes were semiconductors and their energy gap decreased from the single one to the double-walled one. Moreover, with raising the nanotube diameter, the energy gap increased, such that at the most stable double-walled nanotube, its value was about 0.216 eV