Electronic structure and optical properties of the dialkali metal monotelluride compounds: Ab initio study.

Structural parameters, electronic structure and optical properties of the dialkali metal monotelluride M2Te (M = Li, Na, K and Rb) compounds in the cubic antifluorite structure were investigated via ab initio calculations using the all electron linearized augmented plane wave approach based on density functional theory with and without including spin-orbit coupling (SOC). The exchange-correlation interactions were described within the PBEsol version of the generalized gradient approximation and Tran-Blaha modified Becke-Johnson potential (TB-mBJ). Optimized equilibrium lattice parameters are in excellent accordance with existing measured ones. Computed energy band dispersions show that the studied compounds are large band gap materials. Inclusion of SOC reduces the band gap value compared to the corresponding one calculated without including SOC. Determination of the energy band character and interatomic bonding nature are performed using the densities of states diagrams and charge density distribution map. Linear optical function spectra are predicted for a wide energy range and the origin of the dielectric function spectrum peaks are determined.

Variation of sweat sodium and chloride with age in cystic fibrosis and normal populations: further investigations in equivocal cases.

Patients attending cystic fibrosis clinics had sweat sodium and chloride concentrations measured, were reassessed clinically and had DNA studies performed. Sweat test results were compared with a matched control population. In both populations sweat sodium increased with age up to 12 years, and did not change significantly thereafter. The age-related increase was significantly less in the cystic fibrosis group. Sweat chloride increased with age in normal, but not in cystic fibrosis children. After age 12 years there was no age-related change in the normal group, and a fall with age in the cystic fibrosis group. Sweat chloride provided the best discrimination between normal and cystic fibrosis populations and this was particularly important in older subjects. Combining sweat sodium and chloride results did not improve discrimination. Nine patients were identified with equivocal sweat chloride results. DNA studies showed six of these subjects were heterozygous for the delta F508 mutation in the cystic fibrosis gene. Clinical assessment did not always resolve cases with borderline sweat chloride results.