Electronic and optical properties under pressure effect of alkali metal oxides

We report results of first-principles calculations for the electronic and optical properties under pressure effect of Li₂O, Na₂O, Ki₂O and Rb₂O compounds in the cubic antifluorite structure, using a full relativistic version of the full-potential augmented plane-wave plus local orbitals (FP-APW+lo) method based on density functional theory, within the local density approximation (LDA) and the generalized gradient approximation (GGA). Moreover, the alternative form of GGA proposed by Engel and Vosko (GGA-EV) is also used for band structure calculations. The calculated equilibrium lattices and bulk moduli are in good agreement with the available data. Band structure, density of states, and pressure coefficients of the fundamental energy gap are given. The critical point structure of the frequency dependent complex dielectric function is also calculated and analyzed to identify the optical transitions. The pressure dependence of the static optical dielectric constant is also investigated.     

Explicit H1-Estimate for the Solution of the Lamé System with Mixed Boundary Conditions

In this paper we consider the Lamé system on a polygonal convex domain with mixed boundary conditions of Dirichlet-Neumann type. An explicit L² norm estimate for the gradient of the solution of this problem is established. This leads to an explicit bound of the H¹ norm of this solution. Note that the obtained upper-bound is not optimal.     

Computational insights about the dynamic behavior for the inclusion process of deprotonated and neutral aspirin in β-cyclodextrin

A high-efficiency microwave irradiation (MW) assisted protocol was proposed to synthesize series SPE-β-CD with specific degree of substitution (DS) in the sodium hydroxide solution. This protocol provided an eco-friendly way to modify the cyclodextrins with bulky sulfopropyl substituent on the purpose of avoiding organic solvents and high quantities of thermal energy. Temperature and energy distribution became more uniform under the new method accordingly. Therefore, not only the reaction time reduced significantly from over 20 h to a few hours, but also the DS increased up according to ¹H NMR spectroscopy, MS and elemental analysis results. Most importantly, the effects of reaction parameters on DS were compared both under MW method and conventional heating method, and were sufficiently studied to guarantee the aforementioned results could be better reproduced and DS of products could become more specific through the synthesis process. Products structures were characterized by FT-IR, DSC, and ¹³C NMR spectroscopy.     

On a Constant Related to the Prime Counting Function

Let \({\pi(x)}\) be the number of primes not exceeding x. We produce new explicit bounds for \({\pi(x)}\) and we use them to obtain a fine frame for the remainder term in the asymptotic formula of the sum \({\sum_{2\leq n\leq x}1/\pi(n)}\).     

FP-LMTO calculations of elastic and electronic properties of the filled skutterudite CeRu4P12

First-principles calculations have been used to investigate the structural, electronic and elastic properties of the filled skutterudite CeRu₄P₁₂, using the full-potential linear muffin-tin orbital (FP-LMTO) method. The exchange-correlation energy is described in the local spin density approximation (LSDA) using the Perdew–Wang parameterization. The results of the electronic properties show that this compound is an indirect band gap material. A special interest has been made to the determination of the elastic constants since there have been no available experimental and theoretical data. The energy band gaps and their volume and pressure dependence are investigated. Our results of the ground-state electronic properties are found to agree with experimental results.     

FP-LMTO investigations of mechanical stability and high pressure of platinum nitride compounds

We report local density functional calculations using the full potential linear muffin-tin orbital (FP-LMTO) method for binary platinum nitride (PtN), in five different crystal structures, the rock salt (B1), zinc-blende (B3), wurtzite (B4), nickel arsenide (B8), and PbS (B10) phases. The ground state properties such as the equilibrium lattice constant, elastic constants, the bulk modulus and its pressure derivative of PtN in these phases are determined and compared with the other available experimental and theoretical works.Our calculations confirm in the B3 structure that PtN is found to be mechanically stable with a large bulk modulus B=232.45 GPa and at a sufficiently high pressure the B8₁ structure would be favoured.The theoretical transition pressure from zinc blende (B3) to NiAs (B8₁), zinc-blende (B3) to rock-salt (B1) and zinc-blende (B3) to PbO (B10) is determined to be 9.10 GPa, 9.85 GPa and 69.35 GPa, respectively. Our calculation shows also in five different structures for PtN a high bulk modulus is a good indicator of a hard material.     

Elastic,electronic and thermodynamic properties of fluoro-perovskite KZnF3 via first-principles calculations

The elastic, electronic and thermodynamic properties of fluoro-perovskite KZnF₃ have been calculated using the full-potential linearized augmented plane wave (FP-LAPW) method. The exchange-correlation potential is treated with the generalized gradient approximation of Perdew-Burke-Ernzerhof (GGA-PBE). Also, we have used the Engel and Vosko GGA formalism (GGA-EV) to improve the electronic band structure calculations. The calculated structural properties are in good agreement with available experimental and theoretical data. The elastic constants C _ij are calculated using the total energy variation with strain technique. The shear modulus, Young’s modulus, Poisson’s ratio and the Lamé coefficients for polycrystalline KZnF₃ aggregates are estimated in the framework of the Voigt-Reuss-Hill approximations. The ductility behavior of this compound is interpreted via the calculated elastic constants C _ij . Electronic and bonding properties are discussed from the calculations of band structure, density of states and electron charge density. The thermodynamic properties are predicted through the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. The variation of bulk modulus, lattice constant, heat capacities and the Debye temperature with pressure and temperature are successfully obtained.     

Ab-initio calculation of stability and structural properties of cadmium chalcogenides CdS, CdSe, and CdTe under high pressure

The structural phase transformations of Cd chalcogenide compounds (CdS, CdSe, and CdTe) under high pressure are studied using the local approximation to the density functional theory, and the one-electron equations are solved by means of the full potential linear muffin-tin-orbital method. CdS, CdSe, and CdTe are found to have nearly similar behaviour of the structural properties under high pressure. In the CdS compound, thePmmn phase is predicted to be thermodynamically stable after the rock-salt structure, and theCmcm structure is found to be thermodynamically stable before the rock-salt structure in both CdSe and CdTe. The resulting structural properties of the zinc-blende, wurtzite, cinnabar, rock-salt,Pmmn, CsCl,Cmcm, and β-Sn phases for these considered compounds are found to be in agreement with the existing experimental data.     

Hydrostannation of Methyl (Carboxysulfamoyl) Triethylammonium Hydroxide Inner Salt: A New Route to Tributyltin Isocyanate

A synthetically useful and facile method for the synthesis of tributyltin isocyanate is described.     

Straightforward Synthesis of 1,2-Amino Phosphate Diesters and Application to the Synthesis of Novel 1,2-Amino Ether Diesters

A variety of 1,2-amino alcohol diesters 1 reacted smoothly with diethyl chlorophosphate under basic conditions to afford the corresponding 1,2-amino phosphate diesters 2 in excellent yields. These compounds served as useful precursors for subsequent nucleophilic attack by alcohols in an S_N2 fashion to provide 1,2-amino ether diesters 3.