The dielectric constant of barium mono-chalcogenides and their improved band gap results

We have applied Engel-Vosko exchange energy within density functional theory, to calculate the electronic structure and the optical properties of BaX (X = Te, Se, and S) compounds via full potential linearized augmented plane wave method. We have found that this improves the band gap results comparing to our previous work in which we had made use of Perdew et al. exchange energy functional. We have also calculated the dielectric constant of these compounds, using both Perdew et al. and Engel-Vosko schemes. It is shown that Engel-Vosko exchange energy functional leads to a better result. We have also reported the effect of spin-orbit coupling on the results.     

Electronic and optical properties of BaTe, BaSe and BaS from first principles

Electronic and optical properties of barium chalcogenide compounds BaX (X=S, Se and Te) in NaCl crystal structure are calculated using the band structure results obtained through the full potential linearized augmented plane wave (FP-LAPW) method. The exchange correlation potential is treated by the generalized gradient approximation. The real and imaginary parts of the dielectric function ε(ω), the optical absorption coefficient I(ω), the reflectivity R(ω) and the energy loss function are calculated. The calculated results show good agreement with the available experimental results, particularly in the low-energy region of the spectra. Furthermore the interband transitions responsible for the structures seen in the spectra are specified. It is shown that the chalcogen p states and Ba 5d states play a major role in optical transitions as initial and final states, respectively. The effect of the spin–orbit coupling on the optical properties is also investigated and found to be significant, especially in high-energy regions.     

Thermal and mechanical design of tangential hybrid microchannel and high-conductivity inserts for cooling of disk-shaped electronic components

The efficiency of electronic equipment is the cornerstone of technology development. Thermal conditions significantly affect the performance of electronic components. Moreover, mechanical strength, size, and mass are the parameters that impose some limitations. Thus, they should be considered in the high tech industry. Therefore, it is needed to examine both mechanical and thermal behaviors simultaneously. Microchannel and inserted high-conductivity materials are two usual cooling approaches. To improve cooling efficiency and mechanical strength, a new method named Hybrid is introduced here. This method is a combination of microchannel and high-conductivity methods. In this study, the consumed energy, the conductivity ratio of the material with high conductivity, peak temperature, and maximum Von Mises stress have been investigated and analyzed. For the hybrid method, the peak temperature and stress were minimized regarding the volume of high-conductivity change in the tangential direction of the duct. The results showed that the tangential hybrid method could decrease the peak temperature and peak Von Mises stress, up to 40% and 34% in comparison to the microchannel and high-conductivity inserts method.

     

Optical properties of alkaline-earth metal oxides from first principles

This study reports the results of an ab initio electronic and optical calculation of alkaline-earth metal oxides (MgO, CaO, SrO and BaO) in the NaCl crystal structure using the full potential linearized augmented plane wave (FP-LAPW) method within the density functional theory. The exchange-correlation potential is treated by the generalized gradient approximation within the Perdew et al scheme. Moreover, the Engel–Vosko GGA formalism is applied so as to optimize the corresponding potential for band structure calculations. The real and imaginary parts of the dielectric function ?(ω), the optical absorption coefficient I(ω), the reflectivity R(ω) and the energy loss function are calculated by random phase approximation (RPA). The calculated results show a qualitative agreement with the available experimental results in the sense that we can recognize some peaks qualitatively, those due to single particle transitions. Furthermore the interband transitions responsible for the structures in the spectra are specified. It is shown that the oxygen 2p states and metal d states play the major role in optical transitions as initial and final states respectively. The effect of the spin–orbit coupling on the optical properties is also investigated and found to be quite small, especially in the low energy region. The dielectric constants are calculated and compared with the available theoretical and experimental results.