Modulation of optical absorption in m-Fe1-xRuxS2 and exploring stability in new m-RuS2.

A first-principle computational method has been used to investigate the effects of Ru dopants on the electronic and optical absorption properties of marcasite FeS2. In addition, we have also revealed a new marcasite phase in RuS2, unlike most studied pyrite structures. The new phase has fulfilled all the necessary criteria of structural stability and its practical existence. The transition pressure of 8 GPa drives the structural change from pyrite to orthorhombic phase in RuS2. From the thermodynamical calculation, we have reported the stability of new-phase under various ranges of applied pressure and temperature. Further, from the results of phonon dispersion calculated at Zero Point Energy, pyrite structure exhibits ground state stability and the marcasite phase has all modes of frequencies positive. The newly proposed phase is a semiconductor with a band gap comparable to its pyrite counterpart but vary in optical absorption by around 106 cm-1. The various Ru doped structures have also shown similar optical absorption spectra in the same order of magnitude. We have used crystal field theory to explain high optical absorption which is due to the involvement of different electronic states in formation of electronic and optical band gaps. LÓ§wdin charge analysis is used over the customarily Mulliken charges to predict 89% of covalence in the compound. Our results indicate the importance of new phase to enhance the efficiency of photovoltaic materials for practical applications.

Pressure dependent half-metallic ferromagnetism in inverse Heusler alloy Fe2CoAl: a DFT+U calculations.

We report the electronic and magnetic properties along with the Curie temperature (T C) of the inverse full Heusler alloy (HA) Fe2CoAl obtained by using the first-principles computational method. Our calculations suggests that Fe2CoAl is a magnetic metal when treated within PBE-GGA under the applied compressive pressures. However, the implementation of electron-electron (U) (i.e., GGA+U) with varying compressive pressure (P) drastically changes the profile of the electronic structure. The application of GGA+U along with pressure induces ferromagnetic half-metallicity with an integer value of total magnetic moment ∼4.0 µ B per unit cell. The integer value is in accordance with the Slater-Pauling's rule. Here, we demonstrate the variation of semiconducting gap in the spin down channel. The band gap increases from 0.0 eV to 0.72 eV when increasing the pressure from 0 to 30 GPa. Beyond 30 GPa, the electronic band gap decreases, and it is completely diminished at 60 GPa, exhibiting metallic behaviour. The analysis of the computed results shows that the treatment of electron-electron interactions within GGA+U and the application of compressive pressure in Fe2CoAl enables d-d orbital hybridization giving rise to a half-metal ferromagnet. The T C calculated from mean field approximation (MFA) decreases up to 30 GPa and then increases linearly up to 60 GPa.

Electronic, magnetic, optical and thermoelectric properties of Ca2Cr1-x Ni x OsO6 double perovskites.

With the help of density functional theory calculations, we explored the recently synthesized double perovskite material Ca2CrOsO6 and found it to be a ferrimagnetic insulator with a band gap of ∼0.6 eV. Its effective magnetic moment is found to be ∼0.23 µ B per unit cell. The proposed behavior arises from the cooperative effect of spin-orbit coupling and Coulomb correlation of Cr-3d and Os-5d electrons along with the crystal field. Within the ferrimagnetic configuration, doping with 50% Ni in the Cr-sites resulted in a half-metallic state with a total moment of nearly zero, a characteristic of spintronic materials. Meanwhile, the optical study reveals that both ε 1 xx and ε 1 zz decrease first and then increase rapidly with increasing photon energy up to 1.055 eV. We also found optical anisotropy up to ∼14 eV, where the material becomes almost optically isotropic. This material has a plateau like region in the σ xx and σ zz parts of the optical conductivity due to a strong 3d-5d interband transition between Cr and Os. In addition, we performed thermoelectric calculations whose results predict that the material might not be good as a thermoelectric device due to its small power factor.

Electronic properties and low lattice thermal conductivity (κ l) of mono-layer (ML) MoS2: FP-LAPW incorporated with spin-orbit coupling (SOC).

This paper focuses on the electronic and thermoelectric properties of monolayer MoS2. Here, we have examined the structure of MoS2, in which the hole in the center of the hexagonal cage is considered as a void atom, termed 1H-MoS2. Density functional theory (DFT) employing the generalized gradient approximation (GGA) and spin-orbit coupling (SOC) has been used for all calculations. Incorporation of SOC resulted in a significant change in the profile of the band energy, specifically the splitting of the valence band maximum (VBM) into two sub-bands. The "split-off" energy is found to be ∼20.6 meV. The reduction of the band gap with SOC is a prominent feature at the K-K location in the Brillouin zone. The band gap calculated with the GGA is ∼1.75 eV. However, on implementation of SOC, the GGA band gap was reduced to ∼1.68 eV. The frequency-dependent phonon dispersion curve was obtained to analyse the thermodynamical stability. 1H-MoS2 is found to be thermodynamically stable with no imaginary frequency. We report a low value of lattice thermal conductivity (κ l) and low electron effective masses, which are desirable for potential applications in thermoelectric devices.

A theoretical analysis of elastic and optical properties of half Heusler MCoSb (M=Ti, Zr and Hf).

Ab initio calculation of the Elastic and Optical properties of cubic half-Heusler compounds MCoSb (M = Ti, Zr and Hf) are reported using the FP-LAPW approach of the Density Functional Theory. Generalized Gradient Approximation was used as the exchange and correlation potential for investigating these properties. It was found that the Bulk modulus decreases with the increase in temperature and increases with the increase in pressure for all of the three Heusler compounds under study. The Debye's temperature along with compressional, Shear and average elastic wave velocities has also been calculated. The elastic results are compared with the available theoretical and experimental works. The optical investigation of the compounds shows high reflectivity at the infrared region of the photon energy. The imaginary part of the dielectric function reveled the optically non-metallic behavior of the MCoSb compounds, with optical band gap being around 1 eV.

Perception about Medicines among the General Public in the Semi-rural Areas of Nepal.

Background Patients' perceptions and beliefs about medicine are affected by their culture, tradition, socioeconomic status, peer influence, educational level, advertisements among other factors. Objective To explore the perception about medicines among the general public in different semi-rural areas of Nepal. Method Cross-sectional study was conducted at different locations within Kathmandu valley from July 2015 to December 2016; 385 individuals were approached using simple random sampling but only 260, aged 18 years and above, who were taking medicines for their health problems, completed the interviewer-administered survey. Their perceptions about medicines were studied using a structured questionnaire based on the WHO booklet "How to investigate the use of medicines by consumers" and analysed using SPSS version 22. Association between respondents' age, gender, education level and perception were statistically analysed using χ2 test and/or Fisher's exact test and multivariate analysis of variance. Result Sixty-one respondents (23.5%) were in age group 56-65 years. Patients' perceptions of medicine safety based on colour, shape, name of medicine, method of administration, compatibility, etc. was statistically different among respondents with regard to their level of education (p = 0.022). More individuals with lower education believed that expensive medicines were more effective (p < 0.001). Increased level of education made them more aware of negative consequences of reusing previous prescriptions (p=0.039). Conclusion Problems with knowledge about medicines were noted among lesser educated individuals. Based on findings, policy makers may develop educational strategies to increase awareness about medicines.