Narrow Results

Our calculations were conducted within density functional theory (DFT) and density functional perturbation theory (DFPT) using norm-conserving pseudo-potential and the local density approximation. The elastic constants of ${\mathrm{\text{Zn}}}_{1-x}{\mathrm{\text{Be}}}_x\mathrm{\text{O}}$ were calculated, $C_{11}$, $C_{33}$ and $C_{44}$ increase with the increase of Be content, whereas the $C_{12}$ shows a non-monotonic variation and $C_{13}$ decreases when Be concentration increases. The values of bulk modulus $B$, Young’s modulus $E$ and shear modulus $G$ increase with the increase of Be content. Poisson’s ratio $\sigma$ decreases with increased Be concentration. The ductility decreases with increasing Be concentration and the compressibility for ${\mathrm{\text{Zn}}}_{1-x}{\mathrm{\text{Be}}}_x\mathrm{\text{O}}$ along $c$-axis is smaller than along $a$-axis. Phonon dispersion curves show that ${\mathrm{\text{Zn}}}_{1-x}{\mathrm{\text{Be}}}_x\mathrm{\text{O}}$ is dynamically stable (no soft modes). Quantities such as refractive index, Born effective charge, dielectric constants and optical phonon frequencies were calculated as a function of the Be molar fraction $x$. The agreement between the present results and the known data that are available only for ZnO and BeO is generally satisfactory. Our results for ${\mathrm{\text{Zn}}}_{1-x}{\mathrm{\text{Be}}}_x\mathrm{\text{O}}$$(0<x<1)$ are predictions.

Density functional perturbation theory (DFPT) and time-dependent density functional perturbation theory (TDDFPT) calculations were employed to study the molecular and electronic structures, linear and nonlinear optical properties, optical phonon modes and vibrational properties of the interaction of poly(9-vinylcarbazole) (PVK)–small-diameter single-walled carbon nanotube (SWCNT) composites. Our calculations show that the chemical connection between PVK and SWCNTs is only through the relatively weak $\pi$–$\pi$ and $\pi$–H bonds. PVK and SWCNTs have different electron accepting abilities and we believe this is the major factor responsible for the charge transfer processes we observe in the calculations. We notice an increase in polarizability value from 152 a.u. (PVK) to 517 a.u. (PVK–SWCNTs), making the PVK–SWCNT composite an ideal model for applications such as mechanical and optoelectronics. Also, the result of our calculations under the time-dependent density functional perturbation theory hinges on the idea that the large value of the polarizability calculated for our composite model is an attribute which can be inferred to processes of charge transfer. Our finding corroborates the fact that non-covalent functionalization is one of the effective chemical methods by which the nonlinear optical response properties of PVK–SWCNT composite may be enhanced.