STRUCTURAL AND ELECTRONIC PROPERTIES OF Sr(N3)2 UNDER PRESSURE

Structural and electronic properties of Sr ( N 3)2 under pressure up to 120 GPa are studied by means of SIESTA calculation. The pressure–angle as well as the cell parameters relation respect to pressure is employed to study the structural changes under pressure. The obtained N–N bond length at zero pressure is in agreement with the other works. The energy band gap takes on the trend of decreasing below 20 GPa and this trend could result in the reduction of the stability for Sr ( N 3)2 crystal, but at 30 GPa it increases suddenly. And polymorphic transformation is observed. The ionic configuration for Sr ( N 3)2 in the fundamental state is estimated to be Sr +1.200 N -0.200. The charge density of N atom is more sensitive to pressure variation than that of Sr atom.

Simulating Nanoscale Processes in Solids Using DFT and the Quasicontinuum Method

A framework is proposed for the investigation of chemical and mechanical properties of nanostructures. The methodology is based on a two-step approach to compute the electronic density distribution in and around a nanostructure, and then the equilibrium configuration of its nuclei. The Electronic Problem embeds interpolation and coupled cross-domain optimization techniques through a process called electronic reconstruction. In the second stage of the solution, the Ionic Problem repositions the nuclei of the nanostructure given the electronic density in the domain. The new ionic configuration is the solution of a nonlinear system based on a first-order optimality condition when minimizing the total energy associated with the nanostructure. The overall goal is a substantial increase in the dimension of the nanostructures that can be simulated by using approaches that include accurate DFT computation. This increase stems from the fact that during the solution of the Electronic Problem expensive DFT calculations are limited to a small number of subdomains. For the Ionic Problem, computational gains result from approximating the position of the nuclei in terms of a reduced number of representative nuclei following the quasicontinuum paradigm.

A Method of Incorporating the Composition into the Calculation of the Si Kβ X-ray Emission Spectrum of the SiO2 — CaO Binary Glass with the DV-X α Molecular Orbital Calculation

ABSTRACTSi KB X-ray emission spectra of SiO2—CaO binary glasses simulated with the DV-X α molecular orbital calculation were compared with ones measured by EPMA. The composition of the glass has been incorporated in the calculation of the Si 3p partial density of states (PDOS). The Si 3p PDOS, as a function of the CaO content, agreed well with the measured Si Kβ X-ray emission spectra of the 62.4mol%SiO2 – 37.6mol%CaO and 43.3mol%SiO2 – 56.7mol%CaO binary glasses. The present method was found to provide a very useful means of clarifying the change in the ionic configuration of the glass with the metal oxide content.

ELECTRICAL CONDUCTIVITY AND STRUCTURAL INVESTIGATION OF THE SYSTEM Zn1−xCuxMnxFe2−xO4

X-ray, electrical conductivity and infrared absorption studies for the system Zn 1−x Cu x Mn x Fe 2−x O 4 have been carried out. All the compounds in the range 0≤x≤1 show cubic symmetry. It is found that all the compounds of the system possess low mobility values in the order of 10−9 cm 2/ Vsec and conduction is due to hopping process. The electrical conductivity measurements show that the activation energy decreases with increasing concentration of Cu 2+ and Mn 3+ in the crystal lattice. X-ray intensity calculations and IR studies indicated the presence of Zn 2+ at tetrahedral sites, Cu 2+ and Mn 3+ at octahedral sites, and Fe 3+ distributed both tetrahedral and octahedral sites. The probable ionic configuration for the system is suggested as [Formula: see text]

Pair potentials and the bonding energy of d-band metals

A method for decomposing the bonding energy of d-band metals into a sum of pairwise interactions between transition metal ions is presented. The dependence of these pair potentials on the configuration of the ions is examined by evaluating them for several model d-band perfect crystals (sc, bcc, Fcc, and hcp). The results indicate that these pair interactions are not extremely sensitive to the ionic configuration. This suggests that parameterizing the variation of the total energy with ionic configuration in terms of pair potentials may be meaningful for some purposes in transition metals. On the basis of our model calculations, we obtain a pairlike approximate expression for the bonding energy.